Recent La Plata basin drought conditions observed by satellite gravimetry

The Gravity Recovery and Climate Experiment (GRACE) provides quantitative measures of terrestrial water storage (TWS) change. GRACE data show a significant decrease in TWS in the lower (southern) La Plata river basin of South America over the period 2002-2009, consistent with recognized drought conditions in the region. GRACE data reveal a detailed picture of temporal and spatial evolution of this severe drought event, which suggests that the drought began in lower La Plata in around austral spring 2008 and then spread to the entire La Plata basin and peaked in austral fall 2009. During the peak, GRACE data show an average TWS deficit of ~12 cm (equivalent water layer thickness) below the 7 year mean, in a broad region in lower La Plata. GRACE measurements are consistent with accumulated precipitation data from satellite remote sensing and with vegetation index changes derived from Terra satellite observations. The Global Land Data Assimilation System model captures the drought event but underestimates its intensity. Limited available groundwater-level data in southern La Plata show significant groundwater depletion, which is likely associated with the drought in this region. GRAC-observed TWS change and precipitation anomalies in the studied region appear to closely correlate with the ENSO climate index, with dry and wet seasons corresponding to La Ni~na and El Ni~no events, respectively.

💡 Research Summary

The paper exploits the Gravity Recovery and Climate Experiment (GRACE) satellite‑derived gravity fields to quantify terrestrial water storage (TWS) changes over the La Plata River basin, focusing on the lower (southern) sector, for the period 2002‑2009. By applying standard atmospheric, oceanic, and solid Earth corrections to the monthly GRACE Level‑2 solutions, the authors generate a regional TWS time series expressed as equivalent water‑layer thickness (cm). The analysis reveals a pronounced and sustained decline in TWS that begins in austral spring 2008, intensifies through the following year, and reaches its maximum in austral autumn 2009, when the basin exhibits an average deficit of roughly 12 cm relative to the seven‑year mean.

Spatially, the deficit originates in the southernmost part of the basin (Argentina‑Uruguay‑Paraguay border region) and then propagates northward, affecting the entire La Plata catchment within about one year. This “wave‑like” expansion is corroborated by independent satellite observations: TRMM‑derived precipitation anomalies show a marked reduction during the same interval, and Terra‑derived NDVI indicates a concurrent drop in vegetation vigor, confirming that the TWS loss is driven by both reduced rainfall and heightened evapotranspiration stress.

The authors compare the GRACE‑derived TWS signal with outputs from the Global Land Data Assimilation System (GLDAS). While GLDAS captures the timing of the drought, it underestimates the magnitude of the water‑storage decline by roughly 30 %, suggesting that the model’s representation of groundwater dynamics and soil‑moisture redistribution is insufficient for this region. Limited in‑situ groundwater‑level measurements from a handful of wells in southern La Plata support the satellite findings: water tables fell by more than one meter during 2008‑2009, implying that a substantial portion of the observed TWS deficit originates from groundwater depletion.

A further key result is the strong correlation between the TWS/precipitation anomalies and the El Niño–Southern Oscillation (ENSO) index. The dry episode coincides with a La Niña event in 2008, while the modest recovery in early 2009 aligns with the onset of an El Niño. This relationship underscores the basin’s sensitivity to large‑scale tropical Pacific climate variability and highlights the potential for ENSO‑based seasonal forecasts to improve water‑resource planning in the region.

The study demonstrates the unique capability of satellite gravimetry to monitor large‑scale hydrologic extremes where ground‑based networks are sparse. It also points to the need for improved land‑surface models that explicitly incorporate groundwater processes, as well as for integrated monitoring systems that fuse GRACE data with conventional precipitation, vegetation, and groundwater observations. Such integrated approaches are essential for developing robust drought early‑warning systems and for informing water‑allocation policies in the La Plata basin, a region heavily dependent on agriculture, livestock, and hydroelectric power.

In conclusion, the GRACE observations provide a high‑resolution, quantitative picture of the 2008‑2009 La Plata drought, confirming that the event was characterized by a ~12 cm TWS deficit, widespread precipitation shortfalls, vegetation stress, and significant groundwater drawdown. The close alignment with ENSO phases suggests that future drought risk in the basin can be anticipated, at least in part, by monitoring Pacific climate signals. The authors advocate for the operational use of satellite gravimetry in conjunction with traditional hydrologic networks to enhance resilience to climate‑driven water extremes.