How much influence does climate have on water demands? Are water restrictions successful at reducing peak demands during dry summers? This paper will discuss answers to these questions through presentation of climate correction modelling results from New Zealand water suppliers.
It is well known that demand per capita varies significantly across the country and this will be due to a wide range of drivers such as household income, property size, industrial demand, and weather influences. The influence of climate is a significant factor in New Zealand’s municipal water demands, particularly in areas with high garden watering. Hotter and drier summers than normal usually result in higher peak day demands which are often managed through water restrictions.
This paper will present findings from statistical regression analysis of municipal water demands and climate influences using the Water Demand Trends Tracking and Climate Correction Tool. This Excel-based statistical model calibrates demand with climate parameters (e.g. soil moisture index, rainfall and maximum temperature) to identify the influence of climate on demand. The model also calculates the climate-corrected demand which is the demand that would have occurred under normal climate conditions. The tool enables the user to plot and compare predicted demand with actual demand to see if the latter was different. The tool identifies the underlying demand trend without the influence of climate and can assist with analysing the impact of water restrictions and other demand management measures.
Climate corrected demand analysis enables water suppliers to more accurately forecast baseline water demands and have a better understanding of the underlying demand trends and potential demand drivers. These methods will also assist water suppliers to prepare water demand forecasts that meet the recommendations set out by the Office of the Auditor General 2010 report: “Planning to meet the forecast demand for drinking water”.