Assessing the effects of climate change on water resources: the Waimea Plains

Climate change has the potential to cause a variety of effects on water resources. It is necessary to assess the potential effects of climate change on hydrologie systems to provide the information needed to develop rational management strategies to cope with such change. This paper reports on a case study of the Waimea Plains catchment located in the Tasman region, South Island, New Zealand. Two methods were used to assess the effects of climate change: (1) trend analysis of historic climate and hydrologie data from routine monitoring systems using the Mann-Kendall method; and (2) modelling of projected effects as a result of standard greenhouse gas emissions scenarios. Trend analysis results were mixed. Statistically significant trends were noted for some climate and hydrologie variables but not others. Modelling started with regionally downscaled climate projections based on the IPCC Al and A2 emissions scenarios. Modelling projections focused on downstream Waimea River flow and groundwater levels for the critical dry period of a record drought year. Both mechanistic computer modelling (MODFLOW) and artificial intelligence modelling were used. Key inputs for this model, such as rainfall recharge, were obtained from artificial intelligence modelling. Artificial intelligence modelling was also applied directly to project stream flow and groundwater levels. Modelling results were similar for both mechanistic and artificial intelligence models. Water usage increased but the decrease in rainfall recharge of groundwater was largely made up by increased stream recharge. The net result was substantial impact on stream flow but only minor effects on groundwater levels. Recommendations from this study include improved routine monitoring of hydrologie variables and expanded modelling efforts in other catchments under a wide variety of hydrologie and climate change conditions.