Global characterization of hydrological and meteorological droughts under future climate change: The importance of timescales, vegetation‐CO₂ feedbacks and changes to distribution functions

Abstract

There is a strong scientific debate on how drought will evolve under future climate change. Climate model outputs project an increase in drought frequency and severity by the end of the 21st century. However, there is a large uncertainty related to the extent of the global land area that will be impacted by enhanced climatological and hydrological droughts. Although climate metrics suggest a likely strong increase in future drought severity, hydrologic metrics do not show a similar signal. In the literature, numerous attempts have been made to explain these differences using several physical mechanisms. This study provides evidence that characterization of drought from different statistical perspectives can lead to unreliable detection of climatological/hydrological droughts in model projections and accordingly give a “false alarm” of the impacts of future climate change. In particular, this study analyses future projections based on different drought metrics and stresses that detecting trends in drought behavior in future projections must consider the extreme character of drought events by comparing the percentage change in drought magnitude relative to a reference climatological period and rely on the frequency of events in the tail of the distribution. In addition, the autoregressive character of drought indices makes necessary the use of the same temporal scale when comparing different drought metrics in order to maintain comparability. Taking into consideration all these factors, our study demonstrates that climatological and hydrological drought trends are likely to undergo similar temporal evolution during the 21st century, with almost 30% of the global land areas experiencing water deficit under future greenhouse gas emissions scenarios. As such, a proper characterization of drought using comparable metrics can introduce lower differences and more consistent outputs for future climatic and hydrologic droughts.

Global Characterization of the Varying Responses of the Standardized Precipitation Evapotranspiration Index to Atmospheric Evaporative Demand

“…Irrespective of the wide spectrum of uncertainty introduced in this kind of models when reproducing the temporal variability of soil moisture observations (see Ford & Quiring, 2019;Stillman et al, 2016;Yuan & Quiring, 2017), we stress that the enhanced role of AED on plant dryness under low-precipitation periods would not be well-recorded if we only consider soil moisture but we do not assess the AED influence. Moreover, several studies agree that the projections of soil moisture and SPEI for future scenarios are almost identical (see Feng et al, 2017;Vicente-Serrano et al, 2019;Xu et al, 2019), and even comparable to those suggested by PDSI (Dai et al, 2018).…”

“…There are also important statistical issues that should be carefully considered when interpreting drought changes associated with AED. These concerns are mostly related to how drought metrics are calculated (S. M. Vicente‐Serrano et al, 2019). Overall, the different assumptions about the role of AED in drought severity, as revealed by climate drought metrics, are still questionable and deserve much more attention for better interpretation and understanding of drought severity.…”

Unraveling the influence of atmospheric evaporative demand on drought and its response to climate change

“…Therefore, studies focusing on this topic usually merge both concepts when evaluating future projections (Dai et al, ; Scheff, , ). In areas in which an important decline in water availability is projected, it is difficult to separate both phenomena, since most of the values recorded in the projections would correspond to those located in (or below) the lower tail of the probability distribution in relation to the values recorded over the historical period (Vicente‐Serrano,Domínguez‐Castro, et al, ). Therefore, these values would be very anomalous in relation to the historical period.…”

“…Nevertheless, despite large uncertainties in the climate model projections for future scenarios, it should be always considered that climate models themselves are fully coupled atmosphere–land (and ocean) models, which are internally consistent (yet imperfect) representations of the climate system (Milly & Dunne, ; Y. Yang et al, ). In this light, to ensure the consistency between calculated drought indices and climate model themselves is the key for assessing future drought changes based on climate model projections (Vicente‐Serrano, Domínguez‐Castro, McVicar, et al, ).…”

Hydrological Response to Drought Occurrences in a Brazilian Savanna Basin

“…Studies suggest an increase in the intensity and frequency of droughts by the end of the century worldwide due to atmospheric evaporative demand increases, reducing water availability, soil water storage, and agricultural production [15,33,34]. Yet, Santos et al [35] observed a reduction in the water table in the PRB wetlands, downstream of the streamflow gauge station of this study, due to a The most significant meteorological droughts occurred during the hydrological years of 1986/87, 1994/95, 1995/96, 1997/98, 2007/08, and between 2014/15 and 2016/17 in the PRB.…”