10 May 2023

Soil moisture is a key factor in predicting droughts and floods


According to a study from U.S., variation in soil moisture is the crucial factor in understanding extreme phenomena such as droughts and floods and Overcoming uncertainty related to climate change

by Matteo Cavallito


Soil moisture makes it possible to predict the risks associated with droughts and floods by planning ahead for the use of water resources. This is supported by a study from the College of Forestry, Wildlife and Environment at Auburn University in Alabama, the results of which were recently published in the journal Earth’s Future.

The investigation, by a team of researchers led by Auburn professor Sanjiv Kumar, with support from, among others, the U.S. Department of Agriculture and the U.S. National Institute of Food and Agriculture, was based on a large number of surveys. This enabled the authors to process a great amount of data produced by the application of two different models for assessing climate variability.

The moisture factor in soil

The analysis, says a statement from the U.S. university, aims at the simultaneous understanding of climate variation and hydrology and the influence exerted by the water cycle. This research, according to the statement, is one of the first studies capable of simultaneously assessing rainfall variability, soil water storage and vegetation-atmosphere interaction processes.

Over the years, Kumar pointed out, regional-scale drought and flood risk forecasting has been characterized by great uncertainty. At the same time, the issue of climate change and its effects has taken center stage in the debate.

Recently, a report released by the Global Water Monitor Consortium, an initiative of the Australian National University, revealed how global warming has increased the incidence of extreme rainfall concentrated in short periods. Such as that of months characterized by exceptionally low rainfall. Kumar also points out how climate change is reducing the so-called “memory” of the Earth’s surface. To simplify: the general rise in temperatures causes the soil to lose moisture faster on average.

The research

The study examined the change in soil moisture in relation to the effects of the so-called El Niño-Southern Oscillation (ENSO), the phenomenon of periodic warming of the waters of the South Central and Eastern Pacific that occurs on average once every five years between December and January. And which includes among its effects floods in the affected area and droughts in more distant regions.

Well, “Even when global warming is projected to increase ENSO and its teleconnected precipitation variability over North America,” the scientists explain, “we find that the corresponding change in soil moisture variability is relatively small and even decreases”. This seemingly paradoxical phenomenon can be explained by considering how the reduction in surface memory due to global warming “leads to reduced year-to-year persistence of soil moisture variability.”

Droughts and floods

In other words, the increasing variability of rainfall does not seem to affect the fluctuation of soil moisture levels all that much. If we want to understand and predict extreme events, therefore, we should not focus specifically on rainfall trends. But, rather, on changes in soil water concentration.

Indeed, according to Kumar, “the regional mean state (soil moisture) changes are the primary drivers of future drought and flood risks.” For this reason, Janaki Alavalapati, president of the College of Forestry, Wildlife and Environment at Auburn University, says, “Despite the uncertainties presented by climate models, this study’s findings could enhance our ability to adapt to climate change.”