This study presents a method for estimating daily rainfall on a 0.05°latitude/longitude grid covering all of New Zealand for the period 1960-2004 using a second order derivative trivariate thin plate smoothing spline spatial interpolation model. Use of a hand-drawn (and subsequently digitised) mean annual rainfall surface as an independent variable in the interpolation is shown to reduce the interpolation error compared with using an elevation surface. This result is confirmed when long-term average annual rainfall data, derived from the daily interpolations, are validated using long-term river flow data.

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Aims: This research analyzes four climate indices derived from gridded, interpolated data to assess New Zealand's climate structure and variation among wine regions. Methods and results:High resolution gridded data based on 1971-2000 climate normals was used to characterize climate indices depicting viticultural suitability in a geographic information system. The statistical properties of each index were assessed over 21 New Zealand viticulture regions. The results show predominately cool to moderately warm climate suitability in New Zealand, comparable to many European and United States regions. While many viticulture regions have one primary class of suitability, variability of climate within regions can be significant, with some regions containing two to four climate classes, making them suitable for a greater range of cultivars. Conclusion:While the indices depict broad patterns expected over New Zealand, both within and between region variations can be substantial among the indices. However, two indices, Growing Season Average Temperature (GST) and Growing Degree-Days (GDD), are functionally identical, but GST is easier to calculate and overcomes many methodological issues in GDD.Significance and impact of the study: This research provides the basis for evaluating general suitability for viticulture in New Zealand, assists comparisons between viticulture regions in New Zealand and worldwide, and offers growers measures of assessing appropriate cultivars and sites. AbstractRésumé

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.

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°l atitude-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 rootmean-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.

The physiologically based growth model CenW was used to simulate wood‐productivity responses of Pinus radiata forests to climate change in New Zealand. The model was tested under current climatic conditions against a comprehensive set of observations from growth plots located throughout the country. Climate change simulations were based on monthly climate change fields of 12 GCMs forced by the SRES B1, A1B and A2 emission scenarios for 2040 and 2090. Simulations used either constant or increasing CO2 concentrations corresponding to the different emission scenarios. With constant CO2, there were only slight growth responses to climate change across the country as a whole. More specifically, there were slight growth reductions in the warmer north but gains in the cooler south, especially at higher altitudes. For sites where P. radiata is currently grown, and across the full suite of GCMs and emission scenarios, changes in wood productivity averaged +3% for both 2040 and 2090. When increasing CO2 concentration was also included, responses of wood productivity were generally positive, with average increases of 19% by 2040 and 37% by 2090. These responses varied regionally, ranging from relatively minor changes in the north of the country to very significant increases in the south, where the beneficial effect of increasing CO2 combined with the beneficial effect of increasing temperatures. These relatively large responses to CO2 depend on maintenance of the current adequate fertility levels in most commercial plantations. Productivity enhancements came at the expense of some soil‐carbon losses. Average losses for the country were simulated to average 3.5% under constant CO2 and 1.5% with increasing CO2 concentration. Again, there were regional differences, with larger losses for regions with lesser growth enhancements, and lesser reductions in regions where greater productivity enhancements could partly balance the effect of faster decomposition activity.

The relationships between New Zealand regional rainfall and south‐west Pacific pressure patterns are investigated. Principal components of monthly sea‐level pressure are computed from 14 Australasian climate stations and interpreted as physical features of the circulation near New Zealand. Monthly rainfall data at eight New Zealand locations are regressed against these components revealing significant relationships, although the percentage of explanation seldom exceeds 50%. At almost all New Zealand locations the dominant pressure–rainfall relationship is that with the first principal component. The physical interpretation of this component varies slightly from month to month, however, in general it represents the strength of prevailing westerlies or south‐westerlies over New Zealand, as described by the location and intensity of regions of high pressure. Other principal components relate to the direction of airflow over New Zealand, to which rainfall at some stations is very sensitive. The relationships described in this paper further advance the understanding of the large‐scale processes that contribute to the weather and climate of New Zealand. © 1998 Royal Meteorological Society