PIAMDDI Meeting Preparation University of New Hampshire Water Balance Model Richard B. Lammers Danielle Grogan Steve Frolking Water Systems Analysis Group Earth Systems Research Center University of New Hampshire Durham, NH, USA 13-14 December 2013

What happens as the river water moves to the river mouth? Agriculture Evapotranspiration Direct human consumption (Domestic and Industrial) Diversions Dams/Reservoirs Wells/Groundwater mining (Not counting water quality changes…) All estimates or Most estimates? Many studies of glacier contribution use the melt at the mouth of the glacier and convert to sea level equivalent But there are many processes occurring between the glacier and the river outlet

UNH Water Balance Model Structure - Single Grid Cell Irrigation Return Precipitation Evapotranspiration Excess Surface Runoff Snow pack Root Depth Crop 1 Crop 2 Root Zone River Water Daily time step Variable spatial resolution used from global ½ x ½ degree (Lat/Lon) to New Hampshire 500m grid cells Historical and future simulations Variable crop schemes Glacier outflow Inter-basin hydrological transfers Dams/reservoirs Ground water (Baseflow) Deep Soil Zone Irrigation: 31 crops/land cover (sub-grid fractions modeled separately) Water Transport Model (WTM) Unsustainable Irrigation (Fossil ground water)

Global irrigation water demand: Variability and uncertainties arising from agricultural and climate data sets Drive WBM with: Two climate reconstructions (NCEP and CRU; 1963-2002) Two maps of irrigated area (FAO & IWMI) n = 159 countries Minimum Maximum Simulated irrigation water withdrawal (km3 y-1) 1000 2000 Precipitation (mm/y) Irrig. Area 40°N Eq. Precipitation 40°S FAO-reported national annual irrigation water withdrawal (km3 y-1) Irrigated Area (Mha) 2 4 6 8 Wisser et al (2008) Geophysical Research Letters, v.35, L24408

Water Balance/Water Transport Model Runs Major Diversions Water Balance/Water Transport Model Runs Includes: Reservoirs and Irrigation. Irrigation water applied with 100% efficiency (no loss back to system) With and Without Inter-basin Transfers (Diversions) When Diversions turned on (red line) more water is abstracted from rivers for irrigation

Tracking the Benefits of Irrigation Inefficiencies Surface Water  Mined Groundwater (as needed) Rivers Reservoirs Deep Soil Zone crop evapo- transpiration Evaporation Irrigation water withdrawals Inefficiency losses Return flowpaths of irrigation inefficiencies 66% 34%

irrigation water demand (mm/y) 34% efficiency 680 km3/yr

irrigation water demand (mm/y) Mined groundwater (MGW) fraction of demand 34% efficiency 34% efficiency MGW = 48% of demand 680 km3/yr 326 km3/yr

irrigation water demand (mm/y) Mined groundwater (MGW) fraction of demand 34% efficiency 34% efficiency MGW = 48% of demand 680 km3/yr 326 km3/yr 68% efficiency 340 km3/yr

Can increased irrigation efficiency offset irrigation water demand (mm/y) Mined groundwater (MGW) fraction of demand 34% efficiency 34% efficiency MGW = 48% of demand 680 km3/yr 326 km3/yr 68% efficiency Can increased irrigation efficiency offset groundwater mining? 340 km3/yr

irrigation water demand (mm/y) Mined groundwater (MGW) fraction of demand 34% efficiency 34% efficiency MGW = 48% of demand 680 km3/yr 326 km3/yr 68% efficiency 68% efficiency MGW = 52% of demand 340 km3/yr 176 km3/yr MGW use decreases (<50%) but its fraction of total demand increases.

Winners & Losers? In addition to decreasing demand for mined groundwater, would increasing irrigation efficiency shift groundwater exploitation stress? RED: Increased efficiency increases relative reliance on mined groundwater. Gleeson & Wada ERL 2013 >100% over-exploited 90-100% critical 70-90% semi-critical <70% safe

How to integrate? Water Balance Model supplies water volume in space and time. Irrigation =f(plant water demand, existing irrigated crops) Can IAM tell us other factors controlling water demand? - Changes in irrigated regions - Market forces - Technology - Legal Dams/Impoundments/Diversions = f(simple operating rules or specified) Can IAM tell us if (or where) new engineering structures are built? - future energy/water demand - political process Human water use = f(Population) Industrial water use = f(GDP) Can IAM tell us - How populations will change? - How water use technology changes? - Changes in desires/motivations of population for water use?