Predicted NPP spatiotemporal variations in a semiarid steppe watershed for historical and trending climates

• Formulated a continuous time-step model for predicting variations of NPP.
• Analyzed hydrology–soil–vegetation interactions in semiarid steep watershed.
• Showed NPP in the watershed is most likely to increase slightly for a long run.
• Showed spatiotemporal variations of NPP also depends on how climate would change.

Accurate prediction of net primary production (NPP) is very important to understanding cycling of carbon, water, and nutrients as influenced by climate change. However, the existing NPP models do not consider site-specific intrinsic characteristics (e.g., soil properties and topography) and have great limitations in arid and semiarid environment, which is the case of the Balagaer River watershed located in northeastern Inner Mongolia Autonomous Region of China. In those models, the estimation of evapotranspiration (ET), a pivotal variable representing biosphere–climate interactive effects, is oversimplified and thus NPP magnitude and/or trend can hardly be predicted with a satisfactory accuracy. For example, NPP predicted by some of the previous studies were too high and exhibited a trend that is opposite to what was observed. The objectives of this study were to: 1) formulate a better NPP prediction model; 2) use the model to evaluate spatiotemporal variations of NPP and their controlling factors. The evaluation was conducted in the Balagaer River watershed. The model uses the Penman–Monteith formula and a theoretical solution to the Budyko's hypothesis to estimate potential and actual ET, respectively. Also, the model includes CLIGEN as a stand-alone module to generate hypothetical climates using “perturbed” values of monthly statistics that are computed from observed daily data. The application of the model in the study watershed indicated that it well predicted both magnitude and spatiotemporal variations of NPP. The results showed a weak declining trend of NPP over the 56 record years and a clear spatial pattern that matches the site-specific intrinsic characteristics. Further, the results showed that NPP in the study watershed will probably increase slightly or stay stable as a result of climate change.