# Responses of Terrestrial Evapotranspiration to Extreme Drought: A Review
## 3 Evapotranspiration Feedbacks to Drought  
While drought has a significant impact on ecosystems [71], the response of ET to extreme droughs remains uncertain, and results vary among studies, possibly due to different climates, durations of water deficits, and ET assessment methods [72; 73]. [PERSON] et al. [29] reviewed the different responses of ET to drought under various situations. In water-limited regions, soil moisture provides the first-order control on ET [20]. Extreme droughs would limit the availability of water for both soil and rainfall interception evaporation and plants' transpiration by reducing precipitation and soil moisture, especially in transitional regions [20]. Increasing air temperatures and vapor pressure deficits (VPD) enhance ET due to the linear relationship between the temperature and the mean kinetic energy of liquid molecules [21]. In addition, the effect of VPD is nonlinear because an increased VPD will decrease stomatal conductance to minimize water loss via closing stomata [24]. The issue is also supported by the finding that about 29% of the global domain shows a significant increase in ET from 1982 to 2013, mainly driven by the increased air temperature and VPD [73]. In the equatorial region, solar radiation is the dominate factor of ET [74; 75]. Studies have reported that the Amazon rainforest sustains elevated ET during drought periods because of fewer clouds [76; 77]. Terrestrial ET could rapidly decrease due to the widespread plant mortality during a severe drought, and the decline of terrestrial ET could last for years due to changes in the ecosystem structure and functionality [71]. Severe droughs can affect the ecosystem, which involves changes in the species and the community scales and alterations in soil properties. In the species scale, extreme drought result in various changes in species structure, physiology, phenology, and plant defense [71]. For instance, drought can alter the leaf morphology, root density, and growth rate and can alter plant species toward drought-tolerant species. Few studies have explicitly investigated the duration of drought impacts on ET. In general, compared to the C-cycle-related drought impacts, which last for several years, the flux parameters are back to their pre-drought levels within a year [78; 79]. Additionally, [PERSON] et al. [80] and [PERSON] et al. [81] reported that the duration of recovery to pre-drought level tends to be longer for woody species and forests compared to herbaceous/non-woody species and grasslands. Plant mortality may occur during and after the drought, lead \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Name** & **ET Scheme/LSS Scheme** & **Input Data** & **Reference** \\ \hline Observation & AWB-ETH & Atmosphere water balance & GPCP, ERA-Int & [PERSON] et al., 2011 [62] \\ \hline \multirow{4}{*}{Remote Sensing} & MPI-BGC & Empirical & CRU, GPCC, AVHRR & [PERSON] et al., 2009 [63] \\  & PRUNI & Pemnan–Montheith & ISLSC II & [PERSON] et al., 2010 [64] \\  & PT-JPL & Priestler–Taylor & AVHRR, ISLP II & [PERSON] et al., 2008 [65] \\  & CSIRO & Pemnan–Montheith & GPCC & [PERSON] et al., 2010 [66] \\  & MODIS & Pemnan–Montheith & GMAO, MODIS & [PERSON] et al., 2011 [43] \\ \hline \multirow{4}{*}{Reanalysis} & ERA-Interim & TESSEL & ECMWF & [PERSON] et al., 2011 [56] \\  & MERRA & GEOS-5 Catchment LSM & Observations from EOS & [PERSON] et al., 2011 [57] \\  & NCEP\_DOE & NOAH & NOAA, OAR, ESRL PSD & [PERSON] et al., 1996 [58] \\  & JRA-25 & SiB & JMA & [PERSON] et al., 2007 [67] \\ \hline \multirow{4}{*}{LSMs} & GSWP-2 & Aerodynamic, & ISLSC II & [PERSON] et al., 2006 [51] \\  & GLDAS & NLDAS & Observation, Reanalysis & [PERSON] et al., 2004 [52] \\  & Aerodynamic, & & & \\  & WaterMIP & Pemnan–Monteith, & WATCH forcing data & [PERSON] et al., 2011 [68] \\  & [PERSON]–Taylor & & & \\  & MERRA-LAND & Pemnan–Monteith & MERRA reanalysis data & [PERSON] et al., 2011 [69] \\  & NOAN-PF & Pemnan–Monteith & NCEP-NCAR, TRMM, GPCP & [PERSON] et al., 2006 [70] \\ \hline \hline \end{tabular}
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