Shift in precipitation-streamflow relationship induced by multi-year drought across global catchments.

Increases in the intensity and frequency of droughts affected by climate changes induce greater uncertainty in precipitation (P) and streamflow (Q) relationship (P-Q relationship). Here, alteration in P-Q relations were assessed resulted from multi-year drought (≥7 years), lag and amplification effects were analyzed between meteorological and hydrological droughts, and then hydrological legacy induced by droughts were presented using the leaf area index (LAI) and the Horton index (ratio of watershed ET to catchment wetness) in different arid regions of 1210 selected catchments across global catchments. Results show that reduced P causes lower Q in arid regions, while tends to induce a higher Q in humid regions than expected. Generally, the severity and intensity were amplified in hydrological drought compared with its triggering meteorological drought. Interestingly, Q reduction was more likely to be induced by meteorological drought in more arid climates, while more likely to be recovered from Q deficit than meteorological drought in the humid regions. Unexpected, vegetation, stimulated by prolonged meteorological and hydrological droughts, tended to maintain higher LAI and subsequently resulted in a lower Horton index, especially in the humid regions. Combined with a traditional bucket model, a conceptual model was developed to elucidate threshold switching characteristics during the drought propagation, and deduced that vegetation played a vital role in partitioning of P and regulating how the catchment coped with climate changes. These new understanding of the hydrological legacy of meteorological drought provides important insights into hydrological mechanisms and the ability of ecology to regulate hydrological processes.