Andrew Tait

Spatial Interpolation of Daily Potential Evapotranspiration for New Zealand Using a Spline Model

Abstract Potential evapotranspiration (PET) is an important component of water balance calculations, and these calculations form an equally important role in applications such as irrigation scheduling, pasture productivity forecasts, and groundwater recharge and streamflow modeling. This paper describes a method of interpolating daily PET data calculated at climate stations throughout New Zealand onto a regular 0.05° latitude–longitude grid using a thin-plate smoothing spline model. Maximum use is made of observational data by combining both Penman and Priestley–Taylor PET calculations and raised pan evaporation measurements. An analysis of the interpolation error using 20 validation sites shows that the average root-mean-square error varies between about 1 mm in the summer months to about 0.4 mm in winter. It is advised that interpolated data for areas above 500-m elevation should be used with caution, however, due to the paucity of input data from high-elevation sites.

Generating Multiyear Gridded Daily Rainfall over New Zealand

Daily rainfall totals are a key input for hydrological models that are designed to simulate water and pollutant flow through both soil and waterways. Within New Zealand there are large areas and many river catchments where no long-term rainfall observations exist. A method for estimating daily rainfall over the whole of New Zealand on a 5-km grid is described and tested over a period from January 1985 to April 2002. Improvement over a spatial interpolation method was gained by scaling high-elevation rainfall estimates using simulated mesoscale model rainfall surfaces that are generated for short periods in 1994 and 1996. This method is judged to produce reasonable and useful estimates of daily rainfall.

A functional evaluation of virtual climate station rainfall data

Abstract Model simulations are increasingly being used to assess farm performance and its impact on the environment. A crucial input in most of these models is daily rainfall data, which are difficult to obtain for remote areas or if the period required is long. Recently, a new long‐term daily climate dataset for all New Zealand, known as Virtual Climate Station (VCS) data, has become available from NIWA (National Institute of Water & Atmospheric Research Ltd). A reasonable agreement between the VCS and observed data has been reported; nonetheless the effect of the uncertainty in the estimated rainfall on model simulations remains an issue to be examined. In this study we investigated the differences in simulated evapotranspiration, drainage and pasture growth by two models of varying complexity when using VCS or observed rainfall data from several locations around New Zealand. The results showed a general agreement between model outputs whether using observed or VCS rainfall dataseis. Model outputs that are closely related to rainfall events, such as drainage, were more sensitive to deviations in the rainfall dataseis than the indirect outputs, such as evapotranspiration. Data aggregation and correction of bias improved agreement between observed and VCS data and this was reflected in the model outputs. Although short‐term simulations should be analysed with care, overall results were promising. The NIWA VCS rainfall data have the potential to be extensively used in conjunction with simulation models for the assessment of land use and management practices.

The economic implications of climate-induced variations in milk production

Abstract Deviations from normal in New Zealands annual milk production, caused by major climatic variations, have a direct impact on the countrys economy. This study shows that the key climatic variables that positively and negatively affect milk production are rainfall, days of soil moisture deficit, and growing degree days. Production in eastern regions and Southland is also affected by the previous years production, indicating that the effects of “good” or “bad” years can propagate into the following year. The largest negative deviation in milk production in the last 30 years, approximately 10% nationally, was in 1998/99, a La Niña year. However, climatic effects caused by the El Niño Southern Oscillation phenomenon in isolation are shown not to consistently impact on national milk production. Economic model runs using several scenarios of drought‐induced reductions in national milk production of the order of 10% show impacts on private consumption and GDP of between 0.3 and 0.5%. Doubling the reduction in milk production leads to non‐linear economic impacts, with private consumption falling by 1.2% and GDP falling by 1.1%.

The relationship between New Zealand's climate, energy, and the economy to 2025

Abstract This study looks at the effect of current climate variability and projected future climate change to 2025 on New Zealands energy industry (mainly electricity supply and demand) and at the wider economic implications of these effects. Electricity demand is modulated by climate largely through temperature, while electricity supply is modulated largely through rainfall and inflows to the major hydroelectricity‐generating lakes in the South Island. Six climate scenarios are examined with an energy model to determine the change in the demand for energy and the change in the composition of energy supply, especially with regard to the mix of electricity generation. The output from this model is then used as an input to a multi‐industry general equilibrium model of the New Zealand economy. The modelling demonstrates that while the expected effects of projected climate change on the energy industry over the next two decades are reasonably significant, the flow‐on effects from the energy to the wider economy are negligible, albeit slightly favourable. Modelling of the effects of climate variability, which includes unusually cold years, unusually warm years, and variable precipitation, however, shows that unexpected adverse events do have a measurable economic impact, particularly if wage rates are inflexible. Export industries are particularly disadvantaged by higher energy costs, implying a need for adequate reserve generation capacity. Just how much reserve capacity is optimal is a topic for further research. Climate change scenarios to 2050 and 2100 show much greater climatic effects than are expected over the next 20 years. These have not been modelled as the types and costs of electricity generation technologies that might become available beyond 20 years are extremely uncertain.

WMO assessment of weather and climate mortality extremes : lightning, tropical cyclones, tornadoes, and hail

AbstractA World Meteorological Organization (WMO) Commission for Climatology international panel was convened to examine and assess the available evidence associated with five weather-related mortality extremes: 1) lightning (indirect), 2) lightning (direct), 3) tropical cyclones, 4) tornadoes, and 5) hail. After recommending for acceptance of only events after 1873 (the formation of the predecessor of the WMO), the committee evaluated and accepted the following mortality extremes: 1) “highest mortality (indirect strike) associated with lightning” as the 469 people killed in a lightning-caused oil tank fire in Dronka, Egypt, on 2 November 1994; 2) “highest mortality directly associated with a single lightning flash” as the lightning flash that killed 21 people in a hut in Manica Tribal Trust Lands, Zimbabwe (at time of incident, eastern Rhodesia), on 23 December 1975; 3) “highest mortality associated with a tropical cyclone” as the Bangladesh (at time of incident, East Pakistan) cyclone of 12–13 November ...

Potential impact of climate change on Hayward kiwifruit production viability in New Zealand

ABSTRACT Sufficient winter chilling is vital for kiwifruit dormancy release and producing high flower numbers in spring. As global (and New Zealand) average temperatures rise, the risk of insufficient winter chilling increases. This study looks at the potential impact of climate change (considering temperature changes only) on the production viability of the Actinidia chinensis var. deliciosa ‘Hayward’ cultivar of kiwifruit, also known as ‘Hayward’, focusing on the principal growing area of Te Puke in the Bay of Plenty of New Zealand. It is shown that production viability steadily decreases over the coming decades for Te Puke, and becomes generally non-viable by the end of the century under all but the most stringent of global greenhouse gas emissions pathways. There are, however, many other areas of New Zealand that show a potential increase in Hayward kiwifruit production viability over the course of the century.