The pan-tropical response of soil moisture to El Nio
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Abstract. The 201516 El Nio event ranks as one of the most severe on record in terms of the magnitude and extent of sea surface temperature (SST) anomalies generated in the tropical Pacific Ocean. Corresponding global impacts on the climate were expected to rival, or even surpass, those of the 199798 severe El Nio event, which had SST anomalies that were similar in size. However, the 201516 event failed to meet expectations for hydrologic change in many areas, including those expected to receive well above normal precipitation. To better understand how climate anomalies during an El Nio event impact soil moisture, we investigate changes in soil moisture in the humid tropics (between 25) during the three most recent super El Nio events of 198283, 199798, and 201516, using data from the Global Land Data Assimilation System (GLDAS). First, we validate the soil moisture estimates from GLDAS through comparison with in-situ observations obtained from 16 sites across five continents, showing an r2 of 0.54. Next, we apply a k-means cluster analysis to the soil moisture estimates during the El Nio mature phase, resulting in four groups of clustered data. The strongest and most consistent decreases in soil moisture occur in the Amazon basin and maritime southeast Asia, while the most consistent increases occur over east Africa. In addition, we compare changes in soil moisture to both precipitation and evapotranspiration, which showed a lack of agreement in the direction of change between these variables and soil moisture most prominently in the southern Amazon basin, Sahel and mainland southeast Asia. Our results can be used to improve estimates of spatiotemporal differences in El Nio impacts on soil moisture in tropical hydrology and ecosystem models at multiple scales.
