Are Droughts becoming more Extreme and Severe?

Date

08/22/17

Today, prominent scientists throughout the country released a new research article on global patterns of drought recovery. Illinois atmospheric scientist Atul Jain was among the experts who contributed to the report. Jain talked about the study’s findings with News Bureau physical sciences editor Lois Yoksoulian.

What factors are involved in drought recovery? Does everything return to “normal” once water is restored, or does it take time?  

Several factors need to be considered to understand drought recovery processes, such as the initial moisture condition, the amount and timing of precipitation, and the temperature. Variations in carbon dioxide concentrations and biodiversity are also associated with changes in recovery time, but to a lesser extent than post-drought climate conditions.

The way that plants recover from drought has a lasting effect and lag time. This is observed in the way that leaves process CO2, wood characteristics, drought-induced tree mortality and plant productivity. Also, the time to recovery is critical for ecosystem function as well as carbon uptake, and it influences whether ecosystems revert to their initial states or transition to a new state. Because future climate projections exhibit “more extreme extremes,” recovery times will be critical for assessing ecosystem resilience.

In terms of the new study, how is drought recovery time measured?

The recovery time is largely unknown for the vast majority of ecosystems. Several studies have been conducted to evaluate the rate of recovery for various plants types after a severe drought. In our recently published research article, we quantified post-drought recovery time of plant productivity – that is, the amount of carbon plants take from the atmosphere through photosynthesis – on a global scale, using satellite data, ground-based measurement data and land surface model results. We focused on plant productivity because it is the largest carbon exchange for ecosystems, its patterns can be estimated using multiple methods and its sensitivity to drought is well-documented.

Why is it so important to view this from a global perspective, rather than just locally?

Providing a globally consistent picture of drought occurrence and recovery across different ecosystem types can help to characterize historic droughts and thus form a basis for real-time monitoring and prediction, including estimates of drought recovery in different ecosystems, as well as improve our predictions of ecosystem productivity in a rapidly changing climate. Our study shows that drought recovery time varies from immediate to multiple years across gradients of climate, vegetation, disturbance and drought.

What are the key global patterns of drought recovery time?

Our study is based on three independent methods of measurement and provides two key insights into global patterns of drought recovery time: First, across the globe, recovery is longest in the tropics and high northern latitudes. Second, recovery times and the area of ecosystems under active recovery have increased over the 20th century.

How did recovery times change throughout the 20th century?

Multiseasonal and multiyear recovery times increased over the 20th century – from 15 and 20 months in the 1901 decade to 36 and 58 months in the 2001 decade – suggesting that the impacts of drought on ecosystems have been increasing over this period. We found that temperate forests and the tropics, in general, exhibited longer recovery time over the 20th century. Possible mechanisms leading to longer recovery times include more intensive use, and thus quicker exhaustion, of plant available water; or the historical lack of drought events and therefore lack of adaptations to protect against drought.

What does the new data imply about the future?

Given anticipated changes in temperature as well as projected increases in drought frequency and severity for the 21st century, our study strongly suggests longer recovery times in the future, which could increase the vulnerability of these systems to future droughts. This factor is of particular concern in the Amazon, where longer recovery times are the norm. Our findings also indicate a chronic state of incomplete recovery may become the new normal over the remainder of the 21st century, with adverse consequences on how well the land will be able to absorb the excess CO2 in the atmosphere.

To reach Atul Jain, call 217-333-2128; jain1@illinois.edu.

The paper “Global patterns of drought recovery” is available online and from the U. of I. News Bureau.