Anisfeld Water Management Chapter 2.pptx

Slideshow based on Chapter 2 of Water Management: Prioritizing Justice and Sustainability (Island Press, 2024)

1. W ater Management: Prioritizing Justice and Sustainability Chapter 2. Water Availability: Spatial and Temporal Variability © 2024 Shimon Anisfeld https:// watermanagement.yale.edu

2. This chapter covers the basics of how much water is available in different regions, with a focus on hydrologic variability, especially drought. We address questions like these: How much water is available for human use, and how does this vary across the world? How do floods and droughts affect water availability? What can we learn about drought from the paleoclimate record?

3. 1. Global Stocks and Flows 2. Spatial Variation in Water Availability 3. Temporal Variation in Water Availability 3.1. Hydrographs 3.2. Flow Duration Curves 3.3. Flood Frequency Analysis 3.4. Rainfall Intensity-Duration-Frequency Curves 4. Drought 4.1. Defining Drought 4.2. Causes of Drought 4.3. The Great Drought and the Dust Bowl: The Role of Management 4.4. Paleoclimatology and Megadroughts Chapter 2 Table of Contents

4. Chapter 2 Highlights Blue water for human use can come from appropriating renewable flows (rivers and groundwater recharge) or from drawing down non-renewable stocks (lakes and aquifers). Humanity also taps into the flow of green water (the transpiration of soil moisture by plants) by using it to grow rainfed crops. Renewable flows generated by the global hydrologic cycle amount to about 46,000 km 3 / yr of blue water (global runoff) and 71,000 km 3 / yr of green water (terrestrial ET). Water availability is highly variable spatially, and is determined by climate patterns and the flow of runoff within river basins. The temporal variability in runoff can be described using several hydrologic tools—largely rooted in assumptions of stationarity—including hydrographs, flow duration curves, flood frequency analysis, and rainfall intensity-duration-frequency curves. Drought is a complex phenomenon that can devastate societies built around average conditions. Climate variability, land-atmosphere feedbacks, and climate forcing can each play a role in causing and perpetuating drought. The impact of drought on society is determined by the physical hazard (magnitude and extent of drought), but also by societal exposure and vulnerability. Societies are most vulnerable to drought when they push land and water to their limits, and in the process destroy natural resources (such as soils) that can help temper drought’s worst effects. Paleoclimatology has revealed the existence of historical megadroughts, challenging assumptions of climate stationarity. Aridification, rather than drought, is probably a better term for megadrought, since megadroughts are driven by climate forcing rather than just climate variability and demand deep societal change rather than short-term measures.