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An abnormally dry subject: drought

Guest Post by Leena Vilonen, 2021-2022 Sustainability Leadership Fellow, and Ph.D. Candidate in the Department of Biology and the Graduate Degree Program in Ecology at Colorado State University

Over the past two decades, the United States has seen a high increase of dry periods without rain otherwise known as drought across the entire country (IPCC 2014). The western US seems to be particularly affected by this dryness. A scientific study measured the severity of drought across the western US from 2000 to 2022 and found that in 2021 almost 80% of the western part of the US experienced exceptional or extreme drought (Williams et al. 2022). But what does exceptional or extreme drought mean for the US? To put this into a historical context, the last 22 years have been the driest period since the year 800 (Williams et al. 2022). This unprecedented dryness has the potential to have many negative consequences throughout the US. Alarmingly, a drought in 2012 cost the agricultural industry $30 billion (Rippey 2015). Continuing drought could cause even further agricultural losses and have unknown consequences on natural systems such as forests or grasslands. Therefore, drought is an important phenomenon to understand, since it will impact both people and our natural areas.

This leads us to our next question: How do we even define drought? In general, most people define drought as an “abnormally dry period” (Slette et al. 2019). Although what abnormal means is not clear. How can you measure abnormal? Abnormal really depends on where you are looking. As you can see in the map below, different regions in the US have different amounts of rainfall per year. For example, in a desert in Arizona, low levels of rainfall are normal, whereas in wetter areas such as Florida high levels of rainfall are expected. Therefore, abnormal will depend on which part of the country you are talking about. People defining drought will thus rely on the historic climate to determine whether drought is occurring. For example, the Palmer Drought Severity Index (Dai 2019) uses past history of a region to determine what categories drought falls into. This is determined by how different the current climate is (how much rain has fallen that year) compared to how much that region typically receives. If the amount of rainfall is below a certain threshold seen in the past, then that year is defined as a drought.

This leads to our next even larger question: What is causing drought and will it get worse over time? Many possible reasons exist for drought occurring that involve many aspects of the water cycle and weather patterns. But one of the main reasons that drought is getting worse over time is simply climate change. In general, increased carbon dioxide from human activities will lead to higher temperatures. These higher temperatures seem to cause greater unpredictability of rainfall with drier areas experiencing even less rainfall as temperatures rise as these higher temperatures cause high pressure systems that resist rainfall (Dereczynski and Menezes 2017). Higher temperatures also lead to higher evaporation of water from the soil and plants, as well as, lower amounts of snowfall and higher snow melt. Losses of water from the soil and plants will lead to immediate losses of moisture to the atmosphere. Decreases in snowfall and snow pack will further lead to increases in heating, as snow reflects light and decreases the temperature of a system (a place with organisms and the physical environment in which they interact). Losses of this will further lead to higher temperatures in the system. All of this combined will intensify drought as drier systems lead to higher pressure systems that further inhibit rainfall.

This leads us to our last question: What can we do to help prevent drought and the negative impacts of drought? In my opinion, the best way out of this problem is first to understand how drought affects our natural and agricultural systems. Scientists are working on this by studying the effects of natural and experimental drought on regions in the US. This will create an important knowledge base that future policy makers can use to create plans of actions to protect these systems. The next step would be to discover how to create drought-resistant systems. Scientists are working on these sorts of questions now and even have developed solutions such as drought-resistant crops (Martignago et al. 2020) and drought-resistant soil microorganisms that can be added to soil to help aid crops in their growth (Niu et al. 2018). The last step is to combat climate change itself. As discussed in the last paragraph, drought is worsening due to the effects of climate change and thus the greatest way we can prevent future drought is to prevent the worsening of climate change. This is a big task at hand but with the help of scientists and people, we may begin to solve it.


Dai, Aiguo & National Center for Atmospheric Research Staff (Eds). Last modified 12 Dec 2019. “The Climate Data Guide: Palmer Drought Severity Index (PDSI).” Retrieved from

Dereczynski CP, Menezes WF. 2017. 1 – Meteorology of the Campos Basin. In: Martins RP, Grossmann-Matheson GS, eds. Meteorology and Oceanography. Campus, 1–54.

IPCC. 2014. Climate change 2014. Synthesis report. Page Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

Martignago D, Rico-Medina A, Blasco-Escámez D, Fontanet-Manzaneque JB, Caño-Delgado AI. 2020. Drought Resistance by Engineering Plant Tissue-Specific Responses. Frontiers in Plant Science 10.

Niu X, Song L, Xiao Y, Ge W. 2018. Drought-Tolerant Plant Growth-Promoting Rhizobacteria Associated with Foxtail Millet in a Semi-arid Agroecosystem and Their Potential in Alleviating Drought Stress. Frontiers in Microbiology 8.

Rippey, BR. 2015. The U.S. drought of 2012. Weather and Climate Extremes 10:57–64.

Slette IJ, Post AK, Awad M, Even T, Punzalan A, Williams S, Smith MD, Knapp AK. 2019. How ecologists define drought, and why we should do better. Global Change Biology 25: 3193–3200.

Williams AP, Cook BI, Smerdon JE. 2022. Rapid intensification of the emerging southwestern North American megadrought in 2020–2021. Nature Climate Change 2002.

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