Global Hydrology Modelling: Running Multiple Ensembles with the Campus Grid Simon Gosling Walker Institute for Climate System Research, University of Reading Thanks to Dan Bretherton (Reading e-Science Centre) and Nigel Arnell (Walker Institute)

Outline The hydrological model & project background Projected changes in global annual runoff Projected changes in seasonal runoff Projected changes in global water resources stresses

Description of the Hydrological & Project Background

The hydrological model: Mac-PDM Mac-PDM is written in Fortran and simulates river flows across the globe on a 0.5x0.5 degree grid. Input data from global climate models (GCMs): –Rainfall –Temperature –Humidity –Windspeed –Cloud cover

The NERC QUEST-GSI project Aim is to examine the global scale impacts of climate change on the hydrological cycle and water resources. If global temperature was to rise by a certain amount, what would the impacts be? -Investigate impacts for the following 9 prescribed mean global temperature changes relative to present: -+0.5ºC ºC ºC ºC ºC ºC ºC ºC ºC

The NERC QUEST-GSI project The climate data is taken from an ensemble of GCMs to explore the role of climate model structural uncertainty. Source: Collins et al. (2006) Towards quantifying uncertainty in transient climate change. Climate Dynamics 27:

Running on the campus grid x x x x x x x x x x x x x x x x x x x xxxxxxxx UKMO HadGEM1 xxxxxxxx MRI CGCM232A xxxxxxxx INM CM30 xxxxxxxx IAP FGOALS10G xxxxxxxx GISS MODELER xxxxxxxx GISS MODELEH xxxxxxxx GISS AOM xxxxxxxx GFDL CM21 xxxxxxxx CSIRO MK5 xxxxxxxx CNRM CM3 xxxxxxxx CCSR MIROC32MED xxxxxxxx CCSR MIROC32HI xxxxxxxx CCCMA CGCM31T63 xxxxxxxx BCCR BCM20 xxxxxxxx NCAR CCSM30 xxxxxxxx MPI ECHAM5 xxxxxxxx IPSL CM4 xxxxxxxx CCCMA CGCM31 xxxxxxxx UKMO HadCM3 Prescribed Temperature GCM used to provide climate data Running on Linux Desktop: 1 run = 3 hours 9 runs = 27 hours 171 runs = 513 hours (21 days) On the campus grid: 171 runs = 9 hours

Projected Changes in Global Average Annual Runoff

Multiple ensembles for various prescribed temperature changes 9 model runs18 model runs81 model runs Sign of change varies by GCM

The challenge of summarising the results But there are issues with the ensemble mean The ensemble mean

The challenge of summarising the results Number of models in agreement

Projected Changes in the Seasonal Cycle of Average Runoff Mekong Basin & Liard Basin

The Mekong

Changes in sign vary by GCM. Magnitude of changes increase with temperature

The Liard

Projected Changes in Global Water Stress

Calculating stresses A region is stressed if water availability is less than 1000m3/capita/year Therefore stress will vary acording to population growth: –Stress calculated for 3 populations scenarios SRES A1B SRES A2 SRES B2 Stresses calculated for the 2050s with different prescribed warming ( ºC)

Global water resources stresses HadCM3

IPSL CM4 CCSR MIROC32HI Global water resources stresses

HadCM3 IPSL CM4 CCSR MIROC32HI Global water resources stresses

Little uncertainty due to population change but much due to GCM choice

Summary and Conclusions Use of the campus grid has reduced run time from 21 days to 9 hours This allows a comprehensive investigation of climate change impacts uncertainty Results demonstrate: –GCM structure is a major source of uncertainty –Sign and magnitude of runoff changes varies across GCMs –For water resources stresses, population change uncertainty is relatively minor

Thank you for your time Visit