ASSESSMENT OF POSSIBLE IMPACTS OF CLIMATE CHANGE IN AN URBAN CATCHMENT1

ABSTRACT:

Stationarity of rainfall statistical parameters is a fundamental assumption in hydraulic infrastructure design that may not be valid in an era of changing climate. This research develops a framework for examining the potential impacts of time to come increases in short duration rainfall intensity upon urban infrastructure and natural ecosystem of small watersheds and demonstrates this approach for the Mission/Wagg bight watershed in British Columbia, Canada. Nonstationarities in rainfall records are first analyzed with linear regression analysis, and the finded trends are extrapolated to build potential time to come rainfall scenarios. The Storm Water Management design (SWMM) is used to analyze the results of increased rainfall intensity upon design peak flows and to assess subsequent time drainage infrastructure capacity according to the derived scenarios. While the framework provided herein may be modified for cases in which more mingled distributions for rainfall intensity are wanted and more sophisticated stormwater management archetypes are available, linear regressions and SWMM are commonly used in practice and are applicable for the Mission/Wagg inlet watershed. Potential future impacts upon stream health are assessed using manners based on equivalent total impervious area. In bourns of impacts on the drainage infrastructure, the originates of this study indicate that increases in short duration rainfall intensity may be wait fored in the future but that they would not create relentless impacts in the Mission/Wagg bight system. The equivalent levels of imperviousness, however, insinuate that the impacts on stream health could be far more damaging.

(KEY TERMS: climate change; environmental impacts; runoff; statistics; surface water; urban hydrology)

INTRODUCTION

There is growing belong to in both the scientific community and the general public above the possibility of important climatic changes to be paid to increases in radiatively active gases in the atmosphere, a phenomenon commonly referr to as "climate change." In the past hundred the activities of a rapidly expanding and industrializing human population have added significant quantities of heat retaining gases to the atmosphere. For example, the Intergovernmental Panel upon Climate Change (IPCC) estimates that through 2100 increases in greenhouse gases will likely lead to an increase in temperature of between I0C and 350C (Houghton et al., 1996) and an increase in sea horizontal of between 13 and 94 cm (Warrick et al., 1996) The IPCC also reports that warmer temperatures will greatest in quantity likely intensify the hydrological round of years leading to an increase in the precipitation intensity and number of storm incidents (Houghton et al., 1996). While the originates of any one particular climate change investigation should be treated with caution, there is scientific consensus (Oreskes, 2004) that these greenhouse gases have contributed to new climatic changes and will likely force futurity significant changes in the earth's climate. However, considerable uncertainty and difficulty remain in assessing the timing, magnitude, and regional variation in climate change. Hydraulic and water resource engineers and other water professionals are today challenged with designing and assessing subsequent time performance of hydraulic infrastructure that may well be subdue to substantially different discharges and pour volumes than those known today.

Most drainage infrastructure design is based upon the capacity to pass a design discharge, like as the 1-in-100-year flood, or the probable maximum inundation in which the consequence of failure is uttermost In small urban catchments, climate change that shows an increase in precipitation, or more importantly an increase in the intensity of precipitation, will increase the magnitude of the design discharges. single major assumption in the traditional approach of designing infrastructure is stationarity, which is that the statistical parameters of the hydrological variables remain constant above time, without major fluctuations or drawn out term trends. However, if climate change is contributing to drawn out term changes in precipitation or precipitation intensity, this assumption of stationarity becomes erroneous. single example of apparent nonstationarity of a hydrologie time series is the total annual precipitation recorded at the Vancouver International Airport, Canada (Figure 1) Despite the scatter, an increasing stretch is evident and indicates an increase in the mean annual precipitation of about 20 percent since 1940

From the perspective of a practitioner, the moot point becomes how to use historic nonstationary data to design or assess the coming time performance of hydraulic infrastructure. Standard hydrologie techniques of that kind as flood frequency analysis and precipitation oftenness analysis, which form the basis for for a like reason much hydraulic design, all assume stationarity. Is it appropriate to use statistical parameters similar as the mean, standard deviation, and skewnes derived from historical data and assume that they will remain constant above the service life of particular infrastructure? This is significant given that the infrastructure may be required to provide adequate drainage capacity or deluge protection for several decades into the time to come