ClimateChange Assessment Guide.pdf - University of Waterloo

Background13when historic low flows or low aquifer levels occur. Anestablished level of risk is implied in designing thestormwater control system and the water supply systems.Climate change has the potential to modify hydrologicsystems in such a way, that the frequency of significantevents increases beyond historic levels (Figure 2.3,Graph B), thus increasing the risk of too much water ortoo little water and vulnerability to associated systemfailure.defCoping range • 1. variation in climatic stimulithat a system can absorb without producingsignificant impacts (Intergovernmental Panelon Climate Change (IPCC), 2001a); 2. rangeof circumstances within which, by virtue of theunderlying resilience of the system, significantconsequences are not observed (Lemmen andWarren, 2004).Natural aquatic ecosystems adapt autonomously; that is,individuals of various species react automatically to thestresses and opportunities of changing environmentalcues and conditions. Sometimes aquatic ecosystemswill be forced to evolve rapidly with the invasion bynon-native species and the disappearance of locallyindigenous species. The loss of coldwater fisherieshabitat as a result of global warming is an example.While humans can react to social, environmentaland economic conditions, they can also undertakeanticipatory, planned adaptation to climate. Thisadaptation is undertaken with the awareness thatclimate varies or that climate is changing and purposefulplanning and action can reduce vulnerability or riskby explicitly incorporating climate information. Byconsidering the possible impacts of climate change onthe hydrology of a watershed, the range of possibleadaptation strategies (e.g., water conservation, higherdykes, increased floodplain, and water storage) whichexpand the system’s coping range (Figure 2.4) can beexplored.Graph A: Historical time series of river flow. Note that, overthe time period of record, flooding occurs three times andthere is insufficient water to meet demand two times.Graph B: Hypothetical future river flow regime with increasedvariability and trend of increased flow. Note that flooding nowoccurs five times and there is insufficient water to meet demandfive times.Figure 2.3 Schematic of coping range (Lemmen and Warren, 2004)Figure 2.4 Adaptive measures to increase coping range (Lemmen and Warren, 2004)