Droughts are common across the globe, spanning a wide range of climatic settings. As papers in this issue demonstrate, better understanding of when they occur, how long they last, and how their occurrence is being reshaped by climate change in often complex ways is key to predicting and managing their wide-ranging impacts.

Low water levels in Lake Powell, Arizona in 2023. Credit: Scott London / Alamy Stock Photo

Droughts arise from a persistent reduction of moisture, whether this deficit is in the atmosphere, land surface, or agricultural systems. The main culprit is a prolonged interval of below average precipitation, lasting weeks to years, that reduces both direct rainfall and indirect surface water inflows from rivers and other pathways. Elevated temperatures that tip soils towards higher evaporation rates are another driver.

Chance, often a confluence of weather patterns, plays a big role in drought occurrence, but research is showing that climate change is making droughts more severe. Below average precipitation in the summer of 2022 led to one of the worst droughts of the last 60 years in Southern and Central Europe. Hydrological and land surface modelling shows that around 31% of the soil moisture deficit can be directly attributed to enhanced evaporation caused by human-induced global warming1. Consideration of warming trends related to climate change processes are necessary for accurate drought projections.

Flash droughts that can arise in just a few days are especially hazardous. An analysis of global data from the past 70 years shows that extreme heat, and its interaction with preexisting soil moisture, can make flash droughts develop more quickly and last longer2. The effect is more pronounced at high latitudes, revealing how poleward spread of extreme heat can reshape short-term drought risks in previously wet areas.

Droughts can also span decades. The Southwest US is an acute example of an area suffering from a multi-decadal drought, with dry conditions having started in the late 1980s. Recurring La Niña-like sea surface temperature patterns in the tropical Pacific, which modify atmospheric moisture transport to the region, have been proposed to be causes of the extended dryness3.

Papers in this issue of Nature Geoscience, however, present alternative explanations for the Southwest US drought that are linked to anthropogenic influences. In an Article, Yan-Ning Kuo and colleagues propose that the radiative effects of anthropogenic aerosols lead to a persistent North Pacific circulation pattern that dampens precipitation in the Southwest US. Although a transition towards more frequent El Niño events in the future and continuing declines in aerosol pollution may eventually increase regional precipitation, this mechanism is expected to drive moisture deficits for years to come.

In another Article in this issue, Victoria Todd and colleagues place the modern drought in the Southwest US in the context of changes over the past 6,000 years, combining proxy reconstructions and palaeoclimate modelling. They propose that past transient transitions to warmer conditions in the Northern Hemisphere led to atmospheric circulation feedbacks in the North Pacific that in turn led to lower precipitation in the Southwest US. Future anthropogenic warming is expected to reinforce this circulation pattern. Decadal-scale drought predictions must consider a wide array of atmospheric circulation modes like this, which occur naturally but are also modulated by anthropogenic climate change.

As the drivers of drought are coming into clearer view, so are their detrimental impacts. For example, an Article by You and colleagues finds that the effects of climate change — including drought — will lead to declines in agricultural productivity that will make substantial currently cultivated land unsuitable for food production.

This refined understanding of where and when will be critical for communities grappling with the daily effects of drought. Actionable forecasts that adjust as the impacts of climate change come into clearer view will be key to navigating the evolving occurrence of these extreme events.