The authors attempted to develop a simple methodology for estimating daily flow duration curves (FDCs) in island watersheds under humid tropic conditions, to realize better water management in data-limited island watersheds. This study disaggregated a FDC into three parts, namely high, middle and low flow parts and estimated each part independently. Based on Hawaiian watersheds, this study developed a methodology for estimating the high flow part using daily precipitation data and the Curve Number (CN) method, whereas we estimated the middle flow part directly from mean monthly flow (MMF) data. The results for the middle flow part showed the MMF data closely tracking the daily FDCs for nine of the eleven studied watersheds. For the high flow part, the results showed that only after calibration of the CN method, were there significant improvements in estimations. These results suggest it is possible to estimate the middle flow part of the FDC with MMF but the high flow part must use a calibrated CN in the CN method. This study also explored the relationship between calibrated CN and estimated absorption capacity of the studied watersheds to find the possibility of estimating suitable CN of a watershed from its geological characteristics.
We performed a field experiment on throughfall, stemflow, and bamboo culm flow to estimate interception in a deciduous broadleaf forest with different stand structures by separately removing the overstory and understory vegetation. The study area is occupied by oak (Quercus serrata) and chestnut (Castanea crenata) with an understory of chino bamboo (Pleioblastus chino). We established three plots for vegetation control, including an overstory plot (removal of understory), a bamboo plot (removal of overstory), and a control plot (both overstory and understory remained). Throughfall amounts relative to precipitation were 61% in the control plot, 54% in the overstory plot, and 31% in the bamboo plot. Average stemflow in control and overstory plots was 3% of precipitation. The significant difference in throughfall for the bamboo plot may have been caused by the high density of understory vegetation. A large portion of intercepted water is transferred to the ground as bamboo culm flow in the understory beneath the canopy in the control plot and in the bamboo plot. Our experiment highlighted the significance of understory vegetation in altering hydrological processes from canopy to understory vegetation.
Land-use change poses a major threat over much of the La Plata River Basin in South America. Paraguay, with one of the highest deforestation rates in the region, has experienced rapid loss of its natural forests. Such landscape transformation implies changes in vegetation traits that affect exchange of momentum, heat, and moisture between the surface and atmosphere. To understand how the regional climate of Paraguay could be affected by the deforestation that occurred between 1990 and 2000, we ran 1-month long simulations for each November during the 2006–2012 period for a control scenario and a past vegetation scenario. Climate responses to land-cover change differed with location and vegetation. In eastern Paraguay, replacement of forest with farmland increased albedo, leading to an overall lower latent heat and both lower and higher sensible heat fluxes. In western Paraguay, replacement of grassland with farmland slightly increased albedo, reducing the sensible heat and increasing evapotranspiration owing to greater surface soil wetness. Effects of land-use change on precipitation are more likely to change local patterns of precipitation than they are the country’s total monthly precipitation.