(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Water Resources Primary Source: IPCC WG-2 Chapter 3 – Freshwater Resources and Their Management

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Human Activities Affecting Water Resources (modified after Oki, 2005) clear land irrigate? drain? less ET? less precip?

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Human Activities Affecting Water Resources (modified after Oki, 2005) veg. change? soil moisture? more ET? more precip ?

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Drivers of Water Consumption? Population Population Food consumption Food consumption Economic policy (including water pricing) Economic policy (including water pricing) Technology (increased efficiency, increased demand) Technology (increased efficiency, increased demand) Lifestyle (e.g., recreation) Lifestyle (e.g., recreation) Societal value of freshwater ecosystems Societal value of freshwater ecosystems

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Human Vulnerability 25% of population in coastal regions 25% of population in coastal regions - < 10% of renewable water supply - rapid population growth Irrigation Irrigation - > 70% of water withdrawals - > 90% of non-reusable, consumptive use Water-stressed basins have billion people Water-stressed basins have billion people Increased efficiency can yield increased vulnerability! Increased efficiency can yield increased vulnerability!

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Current Water Stress

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Water-Stress Effects AmountTiming - seasonality - drought - flood Quality - salinity - nutrients - temperature - toxins - pathogens - sediments

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) A simple surface water budget Precipitation – Evaporation = Runoff +  Storage storage includes lots of things: soil moisture, aquifers, reservoirs, withdrawals for irrigation, glaciers, snowpack, etc. (From R. Arritt)

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Africa: Geographic Changes Minus (A1B) # models with  > % -50% 21 0

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Africa: Water Balance Changes Minus # models with  > 0

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) South America: Geographic Changes # models with  > % -50% Minus (A1B)

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) South America: Water Balance Changes % -50% Minus # models with  > 0

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Multi-Model Runoff Change A1B Scenario Agree on sign of change? white: < 66% stippled: > 90% (derived from Milly et al. 2005)

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Runoff Change SRES A2 2050s vs Seasonality?

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Groundwater Recharge Using a global hydrological model - WGHM Using a global hydrological model - WGHM

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) What is drought? One definition: One definition: Elements of the definition: Elements of the definition: deficiency of precipitation deficiency of precipitation extended period (how long is "extended"?) extended period (how long is "extended"?) water shortage for some user ("group or activity") water shortage for some user ("group or activity") A deficiency of precipitation over an extended period that causes water shortage for some group or activity.

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Drought depends on the user Crops rely on stored soil water. Soil water can be rapidly depleted, so that monthly droughts may affect crops.

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Drought depends on the user Rivers and streams may dry out during seasonal droughts.

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Drought depends on the user Multi-year droughts may deplete ground water that supports communities. Multi-year droughts may deplete ground water that supports communities.

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Drought, more precisely Must define the time period over which precipitation is below normal. Must define the time period over which precipitation is below normal. Must define what is a water shortage that affects a particular activity. Must define what is a water shortage that affects a particular activity.

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Iowa corn yields 1988 drought 1993 flood

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Recurrence of 100-yr Droughts IS92a emissions IS92a emissions Business-as- usual water scenario Business-as- usual water scenario

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Increased Water Stress

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Runoff Changes - Two Analyses A1B Scenario Agree on sign of change? white: < 66% stippled: > 90% (derived from Milly et al. 2005) (derived from Nohara et al. 2006) ( ) minus ( )

Lake Mead

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Lake Mead Facts Lake Mead was formed in Black Canyon when the Hoover Dam was finished in Water source for over 22 million people. Lake Mead supplies water to: Las Vegas 90% of the supply comes from Lake Mead Los Angeles San Diego Southern California Agriculture Extends 110 miles behind the dam Capacity is 28.5 million acre-feet Saylorville = 641,000 acre-feet

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Lake Running Dry? The Causes Colorado River system is seeing a deficit of Colorado River system is seeing a deficit of 1 million acre-feet of water per year This amount can supply 8 million people for 1 year. This amount can supply 8 million people for 1 year. The water supply is not being replenished The water supply is not being replenished 8 years of continued drought in the region 8 years of continued drought in the region Below average snowfall within the Colorado River watershed Below average snowfall within the Colorado River watershed Human factors Human factors Human demand has increased as populations in the southwest have exploded. Human demand has increased as populations in the southwest have exploded. Increased evaporation off the lake Increased evaporation off the lake Human induced climate change Human induced climate change

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) A Comparison Lake Mead has dropped over 100 feet in the last 10 years to its lowest level since the 1960s. September 1998 June 2008

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Personal Experience (R. C.-G.) A photo I took of the The same view behind 1998 flood at the dam - the dam in June water topped the 8 years of drought and over-use of water spillways for 4 days. May 1998 Las Vegas flood and above average snowfall

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Update: New Record Low (Source: Climate.gov)

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Long-Term Trends (Source:

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Water Cycle Changes - Impacts A1B Scenario (derived from Nohara et al. 2006) ( ) minus ( )

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Water Cycle Changes – AR5 Table for next slide

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Water Cycle Changes – AR5 Observed Impacts

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Water Cycle Changes – AR5 Change in +2˚C: GCM  GHM simulation (from Schewe et al. 2013)

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Water Cycle Changes - AR5  Freq of flood with magnitude of “100-yr flood” Global exposure to 20 C 100-year flood (or greater) [10 6 people] (Hirabayashi et al., 2013)

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Water Cycle Changes AR5 Change in +2˚C

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Water Cycle Changes – AR5 Human vulnerability to decrease in renewable groundwater res. (by 2050s) (from Döll et al. 2009)

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Water Cycle Changes – AR5 Table for figure in next slide

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Water Cycle Changes – AR5

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) Water Cycle Changes – AR5

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Water Resources (from IPCC WG-2, Chapter 3) END Water Resources