Water cycling in a Bornean tropical rain forest under current and projected precipitation scenarios

Abstract

[1] Southeastern Asian tropical rain forests are among the most important biomes in terms of annual productivity and water cycling. How their hydrologic budgets are altered by projected shifts in precipitation is examined using a combination of field measurements, global climate model (GCM) simulation output, and a simplified hydrologic model. The simplified hydrologic model is developed with its primary forcing term being rainfall statistics. A main novelty in this analysis is that the effects of increased (or decreased) precipitation on increased (or decreased) cloud cover and hence evapotranspiration is explicitly considered. The model is validated against field measurements conducted in a tropical rain forest in Sarawak, Malaysia. It is demonstrated that the model reproduces the probability density function of soil moisture content (s), transpiration (T r ), interception (I c ), and leakage loss (Q). On the basis of this model and projected shifts in precipitation statistics by GCM the probability distribution of I c , Q and, to a lesser extent, s varied appreciably at seasonal timescales. The probability distribution of T r was least impacted by projected shifts in precipitation.

An analysis of soil moisture dynamics using multi-year data from a network of micrometeorological observation sites

“…Kumagai et al [44] addressed the issue of soil moisture dynamics and climate change in a tropical rainforest, concluding that at their site, the pdf of soil moisture was not extremely sensitive to the predicted changes in precipitation. Their results are similar to those for Vaira and Walker Branch, where precipitation during the growing season increased, while year-round precipitation remained the same or decreased.…”

“…A 5% increase in R net − G produces an 8% mid-century and a 12% late century increase in E max . Assuming that precipitation and net radiation were related by cloud cover, Kumagai et al [44] fitted an exponential curve to data from a Bornean tropical rain forest. The curve was then used to predict R net from the predictions of future precipitation patterns at the site.…”

Water scarcity and oil palm expansion: social views and environmental processes

“…Also, rubber trees partially shed their leaves in pronounced dry periods, which further reduces transpiration by up to 70% explicitly in times of water scarcity. In addition to the much lower re-evaporation of water to the atmosphere, rainfall interception by rubber plantations is 1.7-fold lower than by oil palm plantations (28% of incident rainfall); our values for interception fall into the range of values reported for tropical forests in South East Asia (commonly 10-30%, e.g., Dykes 1997, Kumagai et al 2004, Dietz et al 2006). The differences in transpiration and interception can explain the lower baseflow from oil palm dominated catchments as compared to rubber dominated catchments that we observed.…”

Scaling up of Carbon Exchange Dynamics from AmeriFlux Sites to a Super-Region in the Eastern United States

“…The model formulation can be shown to reduce to a non-linear ordinary differential equation whose state is stored water in the root zone, the non-homogeneous term is precipitation reduced by interception losses (that vary with LAI), drainage losses that vary as a power-law with stored water and soil texture, and transpiration losses also affected by stored water through the bulk canopy conductance. This model, described in Kumagai et al (2004) has been tested for the 8-year soil moisture record at the Duke Forest Ameriflux site on ½ hourly time scale (see Figure 12). Gabriel Katul, Hans Peter Schmid, Ram Oren, and a post-doctoral fellow at Duke University will conduct this work.…”