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By Daniel Collins

For those of you who don’t receive New Zealand’s own hydrology journal, or for those who want to save some time, here’s an overview of this month’s edition — the journal’s 100th.

1. Barry Fahey (Landcare Research) et al. use their water balance model, WATYIELD, to assess whether tussock in Otago’s uplands can really intercept appreciable amounts of fog, turning it into runoff. Their conclusion: no. This is actually one in a long line of studies that have considered the same question, a question that has turned out to be a veritable controversy, with different papers firmly coming down on opposing sides.

2. Suzanne Poyck (formerly NIWA) et al. use their catchment hydrology model, TopNet, to forecast the impacts of climate change on the Clutha River basin, with a particular focus on changes to snow. Annual precipitation is forecast to increase, as is streamflow (mainly in winter and spring), while the role of snow diminishes.

3. Michael Stewart (Aquifer Dynamics and GNS Science) et al. use isotopic analysis to identify the sources and ages of nitrate in the Waimea Plains, near Nelson. Two kinds of contamination were identified: diffuse contamination from inorganic fertilizers and manure, and point source contamination from a large piggery (now closed). This has been a problem because Ministry of Health guidelines for drinking water have been exceeded for some years. And while input of nitrogen has been decreasing, best practices and nutrient budgeting are still encouraged.

4. Luke Sutherland-Stacey (University of Auckland) et al. test a mobile rain radar device in Tokoroa, central North Island, during 2008 and 2009. Their X-band radar system was able to make observations with high spatial (~100 m) and temporal (~15 s) resolutions, which helps resolve rainfall patterns during convective weather systems at least compared with existing rainfall monitoring systems. But as accuracy declined with distance, particularly over 15 km, the device is best suited for small study areas.

5. Tim Kerr (NIWA) et al. develop a new map of mean annual precipitation for the Lake Pukaki catchment, which includes Aoraki/Mt Cook, using data from 1971-2000. The catchment average is 3.4 m/yr, with over 15 m/yr falling in the north west of the catchment.

6. Clare Sims (BECA) et al. study the dynamics of snowmelt in the Pisa Range, Central Otago. Their focus was how the meteorological conditions that develop over fault-block mountain ranges in the region affect snowmelt. They showed that net radiation (basically sunlight) was slightly more important than sensible heat flux (basically wind), resulting in a sustained pulse of meltwater. They went on to suggest that changes in winter snow could have a significant effect on summer river flows.