A Year in Review: New Earth Discoveries in 2023

Great Salt Lake depicted from the shoreline in the middle left of screen is the water, the foreground has dry and brown vegetation that can be seen curving, mirroring the curve of the water's edge with a seemingly wide expanse of salted dried lake bed between
Great Salt Lake showing the decrease in water level.
NASA / Dorothy Hall

Each year, the Earth Science Division’s Research and Analysis Program combines space, airborne, and ground-based observations with data processing from high-tech computer models and algorithms to uncover new things about the Earth. Explore some of our top discoveries of 2023.

Desiccation of terminal lakes in the Western United States

Terminal lakes in the Great Basin (GB) of the western US host critical wildlife habitat and food for migrating birds Surface and air temperatures in the region are rising dramatically, with a sharp rise in the rate of increase observed beginning around 2011. Rising temperatures coincide with fewer days of snow cover, a decrease of inflow to the lakes and greater evaporation of water from the lakes. MODIS Earth Science Data Records show strong and statistically significant increasing surface temperature, a reduction in the number of days of snow cover, and mixed results in evapotranspiration. Severe and costly ecological, human health and economic consequences are expected if the lakes continue to decline as predicted.

Associated Publication: Hall, D.K., Kimball, J.S., Larson, R., DiGirolamo, N.E., Casey, K.A. and Hulley, G., Intensified Warming and Aridity Accelerate Terminal Lake Desiccation in the Great Basin of the Western United States. Earth and Space Science, p.e2022EA002630. https://doi.org/10.1029/2022EA002630

Detecting landslides in heavily forested regions using long-waveband radar

Rapid technical advancement and global applications of the InSAR (Interferometric Synthetic Aperture Radar) technique in the past two decades has greatly explored and substantiated SAR's value and potential for monitoring earth's surface deformation, ranging from fault slip, volcanic unrest, landslides, glaciers to infrastructure instability.  The relatively short wavelengths (3.1–24.2 cm) of X/C/L-band SAR sensors limit their capability to penetrate through dense vegetation rendering them less effective for surveying densely forested terrains. One possibility is that the 69.72 cm-wavelength P-band SAR could help address these challenges.  Researchers acquired P-band repeat-pass SAR data to assess hazards of densely-vegetated deep-seated landslides over the Pacific Northwest. This study found that P-band, which will be made openly available globally after the launch of NISAR, outperforms L-band data for discovering deformation in densely vegetated terrain. Over 200 new landslides that were missing from existing inventories were identified. This new information will help provide a more complete knowledge base for understanding hazards of landslides over the densely vegetated terrain of the Pacific Northwest and demonstrates some of the increased capabilities we can expect from NISAR.

Associated Publication: Xu, Y., Z. Lu, R. Bürgmann, S. Hensley, E. Fielding, and J. W. Kim (2023), P-band SAR for ground deformation surveying: Advantages and challenges, Remote Sensing of Environment, 287, 113474, https://doi.org/10.1016/j.rse.2023.113474

Satellite-based estimates of national carbon budgets for the Global Stocktake

To meet the carbon dioxide (CO2) emission reduction targets set in the Paris Agreement, there needs to be an accurate accounting of CO2 emissions and removals at the national scale.  A group of researchers presented a pilot project designed to start a dialogue between the top-down research community, inventory compilers and the greenhouse gas assessment community to identify ways that top-down CO2 flux estimates can help inform country-level carbon budgets.  The top-down estimates are based on observations of net atmospheric CO2 concentrations from NASA’s Orbiting Carbon Observatory (OCO-2) provided by the OCO-2 modeling intercomparison project (MIP). These values are further refined with ground level estimates of fossil emission and changes in forest biomass and other carbon stocks.  Between 2015 and 2020 this approach found carbon stored in global terrestrial pools increased by 3.29–4.58 Pg CO2 yr−1 (+ 0.90–1.25 Pg C yr−1), representing about 10% of global fossil fuel emissions.

Associated Publication: Byrne, B., et al., National CO2 budgets (2015–2020) inferred from atmospheric CO2 observations in support of the global stocktake, Earth System Science Data, 15(2), 963-1004, 2023. https://doi.org/10.5194/essd-15-963-2023

Understanding accelerated sea-level rise along the East Coast and Gulf Coast of the United States

Sea-level rise is one of the most severe consequences of a warming climate, threatening hundreds of millions of people living in low-lying coastal communities. Globally, mean sea-level (MSL) has increased by ~1.5 mm yr−1 since 1900, a rise that is unprecedented over at least the last 3000 years and primarily induced by the ocean’s thermal expansion and mass changes due to melting ice sheets and glaciers. Global MSL rise has also been accelerating since the 1960s, reaching values of >3 mm yr−1 since 1992. Along the North American East and Gulf coasts, a combination of natural and man-made vertical land motion has resulted in MSL trends ranging from 1.7 to 8.4 mm yr−1 between 1900 and 2021, causing considerable impacts that include exponential increases in nuisance flooding, increased damages due to major storms and the prospect of accelerating land loss in the most vulnerable settings

These results imply that the early detection of acceleration signals, which are needed for near-term planning and decision-making, still represents a major challenge and that comparisons with climate model projections, specifically locally, need to be undertaken with care. More generally, our findings highlight the critical role of a mechanistic understanding of MSL accelerations at the regional scale and its importance for sea-level projections.

Associated Publication: Dangendorf, S., Hendricks, N., Sun, Q. et al. Acceleration of U.S. Southeast and Gulf coast sea-level rise amplified by internal climate variability. Nat Commun 14, 1935 (2023). https://doi.org/10.1038/s41467-023-37649-9

Evidence that plankton communities are already shifting in response to climate change

Strong natural variability has been thought to mask possible climate-change-driven trends in phytoplankton populations from Earth-observing satellites. A novel approach to measuring ocean color using multivariate remote-sensing reflectance (Rrs) was used to detect climate-change trends. Using a 20-year Rrs time series from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite, over half (56%) of the ocean surface showed significant changes mainly within 40 degrees of the equator. These results suggest that the effects of climate change are already being felt in surface marine microbial ecosystems, but have not yet been detected because previous studies have considered Chlorophyll or other univariate approaches.  The changes in Rrs identified here have potential implications both for the role of plankton in marine biogeochemical cycles and ocean carbon storage, and for plankton consumption by higher trophic levels and thus fisheries.

Associated Publication: Cael, B.B., Bisson, K., Boss, E., Dutkiewicz, S. and Henson, S., 2023. Global climate-change trends detected in indicators of ocean ecology. Nature, pp.1-4. https://doi.org/10.1038/s41586-023-06321-z

Using precipitation measurements from IMERG to improve estimates of soil moisture in sparsely instrumented regions

Soil moisture links the land surface water, energy, and carbon cycles. NASA Soil Moisture Active Passive (SMAP) satellite observations and observation-based precipitation data are merged into a numerical model of land surface water and energy balance processes to generate the global, 9-km resolution, 3-hourly soil moisture data product. The product supports Earth science research and applications, such as flood prediction and drought monitoring.   It was recently shown that utilizing satellite- and gauge-based precipitation inputs from the NASA Integrated Multi-satellitE Retrievals for the Global Precipitation Measurement (IMERG) products, produced as part of the Global Precipitation Measurements (GPM) mission improves the temporal variations in the estimated soil moisture, particularly in otherwise poorly instrumented regions in South America, Africa, Australia, and East Asia. This paper represents the nexus of two flagship NASA missions – SMAP and GPM – and how they can be utilized together to help understand the global water cycle.

Associated Publication: Reichle, R. H., Q. Liu, J. V. Ardizzone, W. T. Crow, G. J. M. De Lannoy, J. S. Kimball, and R. D. Koster, 2023: IMERG Precipitation Improves the SMAP Level-4 Soil Moisture Product. J. Hydrometeor., 24, 1699–1723, https://doi.org/10.1175/JHM-D-23-0063.1.

A potential path to improved tsunami detection and early warning systems using GNSS satellite data

Today more than 700 million people living in coastal areas are at risk from tsunamis and other extreme events like severe storm surges. And this number is likely to grow as coastal populations and oceans rise. Advance warning of impending hazards provides more opportunity people for to evacuate and to safeguard critical infrastructure. Given ocean waves’ relatively slow velocities, the impacts of tsunamis can be forecast and that their propagation across the ocean can be tracked and projected.  Tsunamis are often triggered by earthquakes or volcanic eruptions, many of which produce atmospheric effects. These reach the ionosphere and produce traveling ionospheric disturbances (TIDs) which can be measured by GNSS sensors. With a constellation of the orbiting CubeSats collecting GNSS data, the extent that extreme events perturb parameters such as temperature, moisture, and electron content over space and time can also be measured. TIDs can be detected in the atmosphere before potentially damaging hazards like tsunamis are detected or cause damage on the ground. The method proposed here for atmospheric sensing of disturbances would use measurements from a globally distributed constellation of numerous CubeSats (ideally, in the hundreds) detecting signals from the roughly 100 GNSS satellites currently operating.

Associated Publication: Han, S. C., McClusky, S., Mikesell, T. D., Tregoning, P., & Sauber, J. (2023). Looking to the sky for better tsunami warnings. Eos, 103, 20-23. https://doi.org/10.1029/2022EO220519

M2-SCREAM : A new high-resolution reanalysis product for scientific studies of chemical composition and transport in the atmosphere

Earth's stratosphere contains a number of trace gases that are important for stratospheric chemistry and the planet's radiative budget, and they provide invaluable information about stratospheric dynamics and transport in a changing climate. Here a new high-resolution composition data set produced at NASA's Global Modeling and Assimilation Office, the MERRA-2 Stratospheric Composition Reanalysis of Aura Microwave Limb Sounder (M2-SCREAM) is introduced and evaluated. M2-SCREAM uses high quality data from the Microwave Limb Sounder instrument (2004-present) combined with meteorological information from NASA's MERRA-2 reanalysis. M2-SCREAM provides global three-dimensional distributions of 3-hourly ozone, water vapor, hydrogen chloride, nitric acid, and nitrous oxide. Comparisons with independent satellite data as well as a process-based analysis of the consistency of the assimilated constituent fields with the MERRA-2 dynamics and with large-scale processes documented in the literature demonstrate the utility of M2-SCREAM for scientific studies of chemical and transport variability on time scales ranging from hours to decades.

Associated Publication: Wargan, K., Weir, B., Manney, G.L., Cohn, S.E., Knowland, K.E., Wales, P.A. and Livesey, N.J., 2023. M2‐SCREAM: A Stratospheric Composition Reanalysis of Aura MLS Data With MERRA‐2 Transport. Earth and Space Science, 10(2), p.e2022EA002632. https://doi.org/10.1029/2022EA002632

Impacts of the GRACE and GRACE-FO satellites on the study of water cycles

Satellite observations of the time-variable gravity field revolutionized the monitoring of large-scale water storage changes beginning with the 2002 launch of the Gravity Recovery and Climate Experiment (GRACE) mission. Most hydrologists were skeptical of the satellite gravimetry approach at first, but validation studies assuaged their concerns and high-profile, GRACE-based groundwater depletion studies caused an explosion of interest. Observations from the GRACE and GRACE-FO satellite missions have been used to identify and quantify wet and dry extreme events around the world over the past 20 years. Results reveal that worldwide intensity – a metric that combines extent, duration, and severity of extreme events – is highly correlated with global warming, more so even than with El Nino and other climate indices. Both wet and dry extreme events have become more severe across all four major climate classes which also implies that weather whiplash events have become more severe.  It is likely that the frequency and severity of droughts and pluvials (the opposite of drought) will continue to increase as the planet warms. Already, during 2015-2021, which were the hottest seven years in the modern temperature record through 2021, the frequency of major droughts and pluvials had increased to four per year from three per year in the prior 13 years.  Changes in hydrological extremes have serious consequences on society, economy, environments, and disaster preparation and planning.

Associated Publications: Rodell, M. and J.T. Reager, 2023: Water cycle science enabled by the GRACE and GRACE-FO satellite missions, Nature Water, 1(1), 47-59, 2023. https://doi.org/10.1038/s44221-022-00005-0

Rodell, M., and B. Li, 2023: Changing intensity of hydroclimatic extreme events revealed by GRACE and GRACE-FO, Nature Water, 1(3). https://rdcu.be/c7vQC, https://doi.org/10.1038/s44221-023-00040-5

Li, B. and Rodell, M., 2023. How have hydrological extremes changed over the past 20 years?. Journal of Climate. https://doi.org/10.1175/JCLI-D-23-0199.1x

Impact of the Hunga Tonga volcanic eruption on atmospheric chemistry

The Hunga Tonga-Hunga Ha’apai (HTHH) volcanic eruption on 15 January 2022 is unprecedented in the modern era in both the amount of water vapor injected into the stratosphere (~10% of the normal stratospheric burden) and the depth of penetration (up to 56 km). While this presaged major shifts in stratospheric gas-phase chemistry, the injection of SO2 from HTHH was an order of magnitude lower than the eruption of Mt. Pinatubo in 1991.     Using observations from the Aura Microwave Limb Sounder (MLS), researchers found that  tropical and southern mid-latitude ozone (O3) and hydrochloric acid (HCl) concentrations decreased significantly while ClO and HNO3 concentrations increased in the months following the eruption. The temperature perturbations resulting from the increased water vapor influenced the chemical dynamics. The repartitioning of the Cl species and accompanying losses of ozone were a result of enhancements in ozone loss processes, particularly in the second half of 2022.   Finally, the re-partitioning of HCl in 2022 was primarily due to gas-phase processes, in contrast to changes resulting from heterogeneous reactions on smoke particles in the wake of the Australian New Year’s fires in 2020.

Associated Publication: Wilmouth, D.M., Osterstrom, F.F., Smith, J.B., Anderson, J.G. and Salawitch, R.J, Impact of the Hunga Tonga volcanic eruption on stratospheric composition, Proceedings of the National Academy of Sciences, 2023.  https://doi.org/10.1073/pnas.2301994120

Understanding electrification during winter storm events

Cloud particle probe data and numerical weather prediction output were examined to understand the potential electrification processes for two winter storms that impacted the Northeast region of the United States. During the 7 February 2020 event, the greatest observed electrification was associated with pristine ice crystals and large snowflakes in an environment with little to no liquid water and high collision rates between large ice crystals. Electrification was likely during the earlier stages of the 29–30 January 2022 event—via collisions of graupel and ice hydrometeors in the presence of supercooled liquid water—but became subdued later in the flight due to the reduced number of graupel and ice crystals within the cloud structure. The numerical weather prediction model output from the two events suggested that snow carries the most electrical charge in wintertime stratiform regions

Associated Publication: Harkema, S.S., Carey, L.D., Schultz, C.J., Mansell, E.R., Berndt, E.B., Fierro, A.O. and Matsui, T., 2023. Electrification Within Wintertime Stratiform Regions Sampled During the 2020/2022 NASA IMPACTS Field Campaign. Journal of Geophysical Research: Atmospheres, 128(18),p.e2023JD038708.  https://doi.org/10.1029/2023JD038708

Measuring the effects of protected areas on biodiversity within and outside their boundaries

The United Nations recently agreed to major expansions of global protected areas (PAs) to slow biodiversity declines. However, although reserves often reduce habitat loss, their efficacy at preserving animal diversity and their influence on biodiversity in surrounding unprotected areas remain unclear. Here we combined ground surveys of animal populations with forest structure assessments based on NASA’s Global Ecosystem Dynamics Instrument (GEDI) observations to see whether PAs across mega-diverse Southeast Asia contribute to vertebrate conservation inside and outside their boundaries. Reserves increased all facets of bird diversity. Large reserves were also associated with substantially enhanced mammal diversity in the adjacent unprotected landscape. Rather than generating leakage that deteriorated ecological conditions elsewhere, our results suggest that protected areas benefit biodiversity beyond their boundaries into the surrounding areas. These findings support the United Nations goal of achieving 30% PA coverage by 2030 by demonstrating that PAs are associated with higher vertebrate diversity both inside their boundaries and in the broader landscape.

Associated Publication: Brodie, J.F., Mohd-Azlan, J., Chen, C., Wearn, O.R., Deith, M.C., Ball, J.G., Slade, E.M., Burslem, D.F., Teoh, S.W., Williams, P.J. and Nguyen, A., 2023. Landscape-scale benefits of protected areas for tropical biodiversity. Nature, 620 (7975), pp.807-812.  https://doi.org/10.1038/s41586-023-06410-z

Observations of the 2019 El Niño conditions during the Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex)

The NASA Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex) employed airborne sensors and a host of satellites and surface sensors to characterize the coupling of aerosol processes, cloud physics, and atmospheric radiation within the Maritime Continent’s complex southwest monsoonal environment. The 2019 season exhibited El Niño conditions and associated drought, high biomass burning emissions, and an early monsoon transition allowing for observation of pristine to massively polluted environments. CAMP2Ex’s preliminary results indicate 1) increasing aerosol loadings tend to invigorate congestus convection in height and increase liquid water paths; 2) lidar, polarimetry, and geostationary Advanced Himawari Imager remote sensing sensors can quantify diverse aerosol and cloud properties and their interactions; and 3) high-resolution remote sensing technologies are able to greatly improve our ability to evaluate the radiation budget in complex cloud systems. Through the development of innovative informatics technologies, CAMP2Ex provides a benchmark dataset of an environment of extremes for the study of aerosol, cloud, and radiation processes as well as a crucible for the design of future observing systems

Associated Publication: Reid, J., et al., The Coupling Between Tropical Meteorology, Aerosol Lifecycle, Convection, and Radiation during the Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex), Bulletin of the American Meteorological Society, 104(6), E1179-E1205, 2023. https://doi.org/10.1175/BAMS-D-21-0285.1

Monitoring the accelerated ice loss and its impact on sea-level rise

Ice losses from the Greenland and Antarctic ice sheets have accelerated since the 1990s, accounting for a significant increase in the global mean sea level. By measuring changes in the volume, gravitational attraction, and ice flow of Greenland and Antarctica from space, NASA and ESA monitor ice sheet mass gain, loss, and contribution to sea-level change over time. The Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) combines 50 independent satellite-based estimates of ice sheet mass balance to present a new, reconciled 29-year record of observed ice sheet mass balance. Results indicate that the ice sheets have lost 7,560 billion tons of ice from 1992 to 2020, contributing 21 mm to sea-level rise. Ice sheet mass loss now accounts for a quarter of all sea-level rise - a fivefold increase since the 1990’s. Continuously monitoring the mass balance of the ice sheets and producing annual updates of Greenland and Antarctica mass balance is critical to track their contribution to the global mean sea level, improve understanding of ice sheet response to climate, and constrain projections of future sea-level rise

Associated Publication: Otosaka, I. N., Shepherd, A., Ivins, E. R., Schlegel, N.-J., et al.: Mass balance of the Greenland and Antarctic ice sheets from 1992 to 2020, Earth Syst. Sci. Data, 15, 1597–1616, 2023. https://doi.org/10.5194/essd-15-1597-2023

Patterns in vegetation dynamics in the grasslands of Eurasia over the past 20 years

Grassland ecosystems cover up to 40% of the global land area and harbor over 30% of the global carbon stored in soils. Since the beginning of the 20th century, grassland ecosystems in Eurasia have sustained several extensive and intensive changes in land cover and land use intensity that have triggered long-term changes, often accelerated by climate change. A time series of Landsat scenes and MODIS spectral reflectance data show that over the past 20 years there were two significant shifts in the grasslands vegetation.  First, there was an overall increase in vegetation cover in the grasslands of Eurasia.  At the same time a decrease in the photosynthetic fraction (ie an increase in stems and twigs and a decrease in green leaves as a fraction of the total vegetation) was observed.  A wide range of statistical hypotheses were tested to determine the effect of different variables on changes in grasslands and found that the map-scale significance of responses and relations varied greatly. This complexity highlights the wide range of change drivers and processes in grassland in Eurasia. This approach is scalable and transferable to other time series of satellite data and regions where similar complexity exists.

Associated Publication: Lewińska, K. E., Ives, A. R., Morrow, C. J., Rogova, N., Yin, H., Elsen, P. R., de Beurs, K., Hostert, P., and Radeloff, V. C. 2023.  Beyond “greening” and “browning”: Trends in grassland ground cover fractions across Eurasia that account for spatial and temporal autocorrelation. Global Change Biology, 29, 4620–4637. https://doi.org/10.1111/gcb.16800

Multi-scale observations of drought in the Mekong River Basin

By leveraging satellite-based observations across a range of spatial scales, this study highlights the utility of Earth observations in informing water resources and land management decisions at the regional scale. This work builds up on and complements traditional studies of droughts in two ways (1) most studies focus on use of drought metrics computed using precipitation or evapotranspiration, but this study uses explicitly precipitation, soil moisture and streamflow to track the evolution of the drought (2) most previous studies have focused on large watersheds while smaller watersheds have generally not been studied on an individual basic. We investigated various sensors with different spatial resolutions, including GRACE (100 kilometers), GPM (10 kilometers), SMAP (10 kilometers), and downscaled SMAP soil moisture (1 kilometer).

At the catchment level, we observe a strong correlation between precipitation, soil moisture and streamflow. The availability of 1 km soil moisture observations highlights the ability to make water resources and land management decisions at the local scale. This high spatial resolution information can assist in specific agricultural decisions such as water availability during time of planting and/or harvest. This work can be further refined to include upcoming high resolution surface water satellite products including those that will come from the NASA Indian Space Research Organization (ISRO) Synthetic Aperture Radar (SAR) mission (NISAR).

Associated Publication: Lakshmi, V., Le, M.H., Goffin, B.D., Besnier, J., Pham, H.T., Do, H.X., Fang, B., Mohammed, I. and Bolten, J.D., 2023. Regional analysis of the 2015–16 Lower Mekong River basin drought using NASA satellite observations. Journal of Hydrology: Regional Studies, 46, p.101362. https://doi.org/10.1016/j.ejrh.2023.101362

Predicting severe hail likelihood using satellite observations, model reanalyses and a deep neural network

This paper highlights a first-of-its-kind study in which deep learning is applied to merged reanalysis and pixel-scale satellite-derived parameters to estimate hail likelihood. The authors estimated severe hail likelihood for satellite-identified convective signatures as an initial step toward global application, which would especially benefit regions without a long-term database of weather radar observations.

Associated Publication: Scarino, B., K. Itterly, K. Bedka, C. R. Homeyer, J. Allen, S. Bang, and D. Cecil, 2023: Deriving Severe Hail Likelihood from Satellite Observations and Model Reanalysis Parameters Using a Deep Neural Network. Artif. Intell. Earth Syst., 2, 220042, https://doi.org/10.1175/AIES-D-22-0042.1