OOS 38-9
The application of a meso-scale atmospheric model, TAPM, to generate fine-scale topoclimatic data in support of spatially-explicit treeline investigations
A significant hindrance to carrying out treeline research over large spatial domains is the relative unavailability of climatic data at local scales. A prominent issue is that topographic complexity in mountainous areas has a major impact on local climates, inducing topoclimatic effects such as aspect-related variation in insolation, valley and slope winds, and cold air drainage and ponding. These topographic effects on mountain climates are virtually impossible to account for using the long-term, interpolated climatic datasets that are typically available. For this study, I assessed whether a meso-scale atmospheric model, TAPM, was able to generate accurate 200 m resolution, hourly topoclimatic data for temperature, incoming and outgoing radiation, relative humidity, and wind speeds. The performance of TAPM was evaluated against available weather station data at mountain sites. As a demonstration of TAPM’s applicability to treeline research, I then used TAPM to generate topoclimatic variables at a range of Nothofagus treeline zones across New Zealand. TAPM-derived data were used to develop indices of winter and summer desiccation, photoihibition, frost, and insolation at treelines. Mixed-effects regression modelling was used to determine the relative influence of regional-scale factors, landform-related effects, and topoclimatic indices on local treeline variation.
Results/Conclusions
Initial assessments of TAPM outputs against data from two climate station locations over seven years showed that the model could generate predictions with a consistent level of accuracy for both sites, and which agreed with other evaluations in the literature. Mixed effects modelling results showed that treelines were generally closer to their site-level maximum in regions with higher mean growing season temperatures, larger mountains, and lower levels of precipitation. Within sites, higher treelines were associated with higher solar radiation and lower photoinhibition and desiccation index values in January and desiccation index values in July. Higher treelines were also significantly associated with steeper, more convex landforms. This study suggests that portable atmospheric models, such as TAPM, can provide a reliable source of topoclimatic data for treeline research. This approach could thus help support spatially- and temporally-explicit investigations of treeline pattern and process at any location.