Abstract
Recent studies showed that anomalous dry conditions and limited moisture supply roughly between 1998 and 2008, especially in the Southern Hemisphere, led to reduced vegetation productivity and ceased growth in land evapotranspiration (ET). However, natural variability of Earth’s climate system can degrade capabilities for identifying climate trends. Here we produced a long-term (1982–2013) remote sensing based land ET record and investigated multidecadal changes in global ET and underlying causes. The ET record shows a significant upward global trend of 0.88 mm yr−2 (P < 0.001) over the 32-year period, mainly driven by vegetation greening (0.018% per year; P < 0.001) and rising atmosphere moisture demand (0.75 mm yr−2; P = 0.016). Our results indicate that reduced ET growth between 1998 and 2008 was an episodic phenomenon, with subsequent recovery of the ET growth rate after 2008. Terrestrial precipitation also shows a positive trend of 0.66 mm yr−2 (P = 0.08) over the same period consistent with expected water cycle intensification, but this trend is lower than coincident increases in evaporative demand and ET, implying a possibility of cumulative water supply constraint to ET. Continuation of these trends will likely exacerbate regional drought-induced disturbances, especially during regional dry climate phases associated with strong El Niño events.
Highlights
Land ET plays a vital role linking global water, energy, and carbon cycles, and is controlled by environmental factors and vegetation dynamics
Demand is quantified by a calculated potential ET rate that only depends on variabilities of air temperature, air vapor pressure, and wind speed, while supply and energy are determined by precipitation and solar radiation, respectively
We obtained gauge and satellite based global monthly precipitation from three independent sources and used these data with the ET and potential ET (PET) records produced in this study to investigate changes in the global terrestrial water availability (TWA) and climatic water deficit (CWD) over the 32-year period
Summary
Ke Zhang[1,2,3], John S. Terrestrial precipitation shows a positive trend of 0.66 mm yr−2 (P = 0.08) over the same period consistent with expected water cycle intensification, but this trend is lower than coincident increases in evaporative demand and ET, implying a possibility of cumulative water supply constraint to ET. Continuation of these trends will likely exacerbate regional drought-induced disturbances, especially during regional dry climate phases associated with strong El Niño events. We obtained gauge and satellite based global monthly precipitation from three independent sources and used these data with the ET and PET records produced in this study to investigate changes in the global TWA and CWD over the 32-year period
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