Ecosystem Productivity and Water Stress in Tropical East Africa: A Case Study of the 2010–2011 Drought

Abstract

Characterizing the spatiotemporal patterns of ecosystem responses to drought is important in understanding the impact of water stress on tropical ecosystems and projecting future land cover transitions in the East African tropics. Through the analysis of satellite measurements of solar-induced chlorophyll fluorescence (SIF) and the normalized difference vegetation index (NDVI), soil moisture, rainfall, and reanalysis data, here we characterize the 2010–2011 drought in tropical East Africa. The 2010–2011 drought included the consecutive failure of rainy seasons in October–November–December 2010 and March–April–May 2011 and extended further east and south compared with previous regional droughts. During 2010–2011, SIF, a proxy of ecosystem productivity, showed a concomitant decline (~32% lower gross primary productivity, or GPP, based on an empirical SIF–GPP relationship, as compared to the long-term average) with water stress, expressed by lower precipitation and soil moisture. Both SIF and NDVI showed a negative response to drought, and SIF captured the response to soil moisture with a lag of 16 days, even if it had lower spatial resolution and much smaller energy compared with NDVI, suggesting that SIF can also serve as an early indicator of drought in the future. This work demonstrates the unique characteristics of the 2010–2011 East African drought and the ability of SIF and NDVI to track the levels of water stress during the drought.

Spatiotemporal Change Analysis of Soil Moisture Based on Downscaling Technology in Africa

“…In the spring, the rate of the s nificant increase in SM was relatively high, except in some areas of region IV, the are The SM contents increased significantly in the coastal regions close to the Indian Ocean, the Mediterranean Sea, the Red Sea, and the area close to Lake Victoria in Africa. The main reason for this is the change in rainfall during the dry season in Africa due to the influence of the ENSO phenomenon [70,71]. ENSO has a substantial impact on weather factors, and contributes to drought (soil moisture) throughout the world [72], which often affects agricultural droughts in South Africa [73].…”

Drivers of Subseasonal Forecast Errors of the East African Short Rains

“…Floods and droughts have significant impacts on lives and livelihoods in East Africa (e.g., Conway et al, 2005;Haile et al, 2019;Little et al, 2001). The short rains from October to December (OND) show substantial interannual variability and extreme impacts from both flooding (e.g., in 2019; Wainwright et al, 2021) and drought (e.g., in 2010; Robinson et al, 2019). Numerous studies have demonstrated skill in predicting the short rains at seasonal scales (Hastenrath et al, 2004;MacLeod, 2018;Mwangi et al, 2014;Ogutu et al, 2017;Philippon et al, 2002;Young & Klingaman, 2020).…”

Editorial for Special Issue: “Global Vegetation and Land Surface Dynamics in a Changing Climate”

“…Managing these ecosystems for current and future changes requires an improved understanding of these multiscale drivers of vegetation dynamics, the mechanisms by which they operate, and how they change over time. This special issue in Land draws together a collection of five articles covering geographic regions in Africa, Asia and North America [14][15][16][17][18]. Taken together, these articles encompass a wide range of study spanning the biophysical drivers (e.g., hydrological) of vegetation change and dynamics and the human impacts (e.g., perceptions of climate change effects) in both natural and managed ecosystems.…”

“…The emergence and proliferation of satellite-based products can offer a variety of ways to monitor ecosystem change in the highly-variable East African climate, but there is a need to better understand how these products capture important ecosystem stress signals. To address this need, Robinson et al [18] analyze how the normalized difference vegetation index (NDVI) and the solar-induced chlorophyll fluorescence (SIF) capture one of the more exceptional, recent drought periods in East Africa: the failure of both the 2010 "short" and 2011 "long" rainy seasons. They further provide a mechanistic characterization of the drought's temporal evolution, contextualizing it within regional anthropogenic climate trends.…”

“…Robinson et al's analysis also highlights how reduced rainfall in one season, in this case the 2010 short rains, can compound the effects of regional drought during the subsequent long rains, exacerbating water-stress impacts to both natural and human ecosystems. This is an important temporal dynamic to better understand and monitor, as the Indian Ocean continues to warm and interact with other oceanic and atmospheric variability and change, thereby changing East African regional atmospheric circulation patterns and moisture convergence [18].…”