Large-scale biospheric drought response intensifies linearly with drought duration in arid regions

Abstract

Abstract. Soil moisture droughts have comprehensive implications for terrestrial ecosystems. Here we study time-accumulated impacts of the strongest observed droughts on vegetation. The results show that drought duration, the time during which surface soil moisture is below seasonal average, is a key diagnostic variable for predicting drought-integrated changes in (i) gross primary productivity, (ii) evapotranspiration, (iii) vegetation greenness, and (iv) crop yields. Drought-integrated anomalies in these vegetation-related variables scale linearly with drought duration with a slope depending on climate. In arid regions, the slope is steep such that vegetation drought response intensifies with drought duration, whereas in humid regions, it is small such that drought impacts on vegetation are weak even for long droughts. These emergent large-scale linearities are not well captured by state-of-the-art hydrological, land surface, and vegetation models. Overall, the linear relationship of drought duration versus vegetation response and crop yield reductions can serve as a model benchmark and support drought impact interpretation and prediction.

Response of Gross Primary Productivity to Drought Time‐Scales Across China

“…This means that plants respond to drought in complicated manners rather than in a linear relationship. Nevertheless, our conclusions are still robust because vegetation growth linearly responds to drought at a large scale, and the linearity may intensify with drought time-scales (Orth et al, 2020).…”

Soil moisture signature in global weather balloon soundings

“…Figure 4d-i shows that, according to the CLASS4GL simulations, in water-limited conditions, the ABL warms (2.72 K), dries (0.86 kPa) and, most notable, deepens (409 m) more during daytime than in energy-limited conditions. Strong differences in height are found due to higher heat capacities of deeper waterlimited ABLs 37,44 . Despite higher moisture input through evaporation in energy-limited conditions, we find that diurnal VPD increases driven by the temperature increase during the course of the day.…”

“…Using remotely sensed soil moisture induces noise in this relationship, as (i) surface soil moisture only represents part of the depth that is relevant for evaporation, and (ii) surface and root-zone are known to decouple in dry conditions 42,43 . Nevertheless, this product is the only global observational soil moisture with an adequate time period available and has been used successfully in similar applications before 38,44 . Figure 3a illustrates that the energy flux partitioning is strongly regulated by soil moisture, even at the landscape scale, as the ratio between latent heat flux and surface available energy (the sum of sensible and latent heat flux) changes from dry to wet soils.…”

Precipitation–productivity relationships and the duration of precipitation anomalies: An underappreciated dimension of climate change

“…Indeed, long‐term studies allude to the strong potential for nonlinear NPP responses to emerge as the duration of PPT anomalies increases (Brando et al, 2008; Goulden & Bales, 2019; Knapp et al, 2012; Liu et al, 2020). This suggests that the duration of PPT anomalies, such as lengthened periods of drought stress projected with climate warming (IPCC, 2013; Naumann et al, 2018; Orth et al, 2020; USGCRP, 2017), could be a key dimension of climate change that will alter future PPT–NPP relationships.…”