Climate Change Impacts on the Water Cycle Emmanouil Anagnostou Department of Civil & Environmental Engineering Environmental Engineering Program UCONN 2014 NECPUC Annual Symposium, Stowe, Vermont

Global surface temperature anomalies relative to average for (a) annual and 5-year running means through 2010, and (b) 60-month and 132- month running means through July Green bars are 2-σ error estimates. ( Credit: James Hansen, NASA GISS & Columbia University ) Global Surface Temperature 2014 NECPUC Annual Symposium, Stowe, Vermont

Impacts on Evaporation and Transpiration (ET) ET increases globally by approximately 2-4%/˚C, as a result of – Increased availability of net radiative energy at the surface – Increased atmospheric demand for evaporation, due to the increased capacity of the atmosphere to hold moisture (by ~7%/˚C per the the Clausius-Clapeyron relationship) 2014 NECPUC Annual Symposium, Stowe, Vermont

Impacts on Precipitation Amount & Characteristics Global average increases: 2-4%/˚C Increase of flooding risk due to increase in rain volumes 2014 NECPUC Annual Symposium, Stowe, Vermont

Impact on Precipitation Characteristics (cont’d) Decrease of rain frequency and/or duration – Increase in the number of consecutive dry days  droughts 2014 NECPUC Annual Symposium, Stowe, Vermont

The most important spatial pattern (top) of the monthly Palmer Drought Severity Index (PDSI) for 1900 to The time series (below) accounts for most of the trend in PDSI. Drought patterns are changing Mainly decrease in rain over land in tropics and subtropics, but enhanced by increased atmospheric demand for evapotranpiration with warming

Most areas of the U.S.: relative increases in precipitation ranging from 9-31%; northeastern U.S.: precipitation increase ~67% Discharges are expected to increase, and with it the flood risk! - Collins et al. 2009: 25/28 New England gauges show upward trends in peak discharges - Wake & Markham 2005; Hayhoe et al (using VIC) Greater winter discharge and earlier shift of peak flows Hydrologic Extremes in the NE USA 2014 NECPUC Annual Symposium, Stowe, Vermont

Suitable for application in cold environments: seasonal and permanently frozen soils, snowpack on ground and canopy Provided by Dr. Fischer from the NASA Jet Propulsion Laboratory Regional Hydrologic Modeling 2014 NECPUC Annual Symposium, Stowe, Vermont

Relative change from 1950 to 2011 in the amount of precipitation falling on days with precipitation exceeding the 99 th percentile of daily precipitation, where the 99 th percentile is estimated using as the reference period. This change is based on the value for 1950 and 2011 derived from linear regression with time, instead of the actual value in these two years Basin Average change: ~240% large values found in the 21 st Century are highly influential Fraction of total: increased by Some things we may expect: larger runoff ratios (flooding), greater peak discharge, soil moisture diminished, exacerbated drought conditions  however, region specific 2014 NECPUC Annual Symposium, Stowe, Vermont

Runoff ratio: basin average increase of – 10% relative increase Trends - Basin Mean SeasonPrecipitation Evapotran- spiration Runoff Soil Moisture DJF mm/day/yr mm/day/yr mm/day/yr 3.67*10 -5 vol. fraction/yr MAM mm/day/yr mm/day/yr mm/day/yr 5.36*10 -5 vol. fraction/yr JJA mm/day/yr mm/day/yr mm/day/yr 1.86*10 -4 vol. fraction/yr SON mm/day/yr mm/day/yr mm/day/yr 1.82*10 -4 vol. fraction/yr Annual mm/yr/yr mm/yr/yr mm/yr/yr 1.15*10 -4 vol. fraction/yr 2014 NECPUC Annual Symposium, Stowe, Vermont

Future Projections ( ) 2014 NECPUC Annual Symposium, Stowe, Vermont

These signals of increased duration and 5 day maximum precipitation are indicators of increased flood severities (e.g. 100 yr return flood) 2014 NECPUC Annual Symposium, Stowe, Vermont

Greatest Change in the water budget variables has been to ET Potentially entering a new regime characterized by increasing ET Climate warming could increase risk of both extreme floods and/or drought Evapotranspiration 2014 NECPUC Annual Symposium, Stowe, Vermont

Globally we expect both drought and flood risk changes due to changes in the precipitation patterns. The NE USA has been experiencing an increasingly wet regime during the latter part of the 20 th century through early 21 st century – indications of change towards more extreme precipitation, increasing discharge, increasing runoff ratio and negligible trend in ET Flood Risk Significant increases in precipitation extremes have been almost entirely accounted for by increases to runoff  Flood Risk How do these trends continue or change in the mid 21 th Century? Precipitation extreme indicators remain statistically similar to early 21 th century major events (100 yr return floods) present a greater risk Flood Frequency has decreased, but the largest storms produce floods that persist for longer durations  major events (100 yr return floods) present a greater risk possible acceleration of the hydrologic cycle NE has gone from a slightly increasing ET trend to a large increase (~8% in the summer)  possible acceleration of the hydrologic cycle greater drought and flood risks It is possible the NE US will enter a new climate regime characterized by greater drought and flood risks Conclusions 2014 NECPUC Annual Symposium, Stowe, Vermont