The few previous studies of precipitation isotopes (δ18O and δD) in Indonesia, based on low spatial resolution observation datasets, have found several types of patterns in their seasonal variabilities. This study conducted high spatial resolution rainfall sampling and investigated the temporal characteristics of precipitation isotope in Indonesia. Rainfall samples were collected weekly from 33 stations in Indonesia. Cluster analysis showed that Indonesia could be divided into four types based on the seasonal variability of the precipitation of δ18O. The majority of stations showed seasonal patterns in the variability of δ18O, characterized by high values in the dry season (July–October) as type 1. Type 2 also showed one peak of high δ18O but in the longer period (June–November) was similar to type 1 stations. A region of Northwest Indonesia, comprising North and Central Sumatra and western Borneo, was identified as type 3, having two peaks of high δ18O values in January–February and May–August. Another pattern of variability was the anti-monsoonal type, indicated by low δ18O in May–July found in east part of Indonesia. Asia-Australia monsoon regime was the main factor that controls seasonal δ18O variability. This research showed that stable isotope in precipitation could correspond to precipitation climatology in Indonesia.
Jakarta is facing several issues related to flooding, including land subsidence in the coastal area and rapid land-use/cover changes in the upstream area. In this study, we analyzed the effects of future changes in land use and land subsidence using a rainfall-runoff and flood inundation model. The future land-use scenarios were projected based on the SLEUTH model, and land subsidence was projected based on an extrapolation of the current state in Jakarta.
Based on this analysis, land-use changes and land subsidence contributed to an increase in flood inundation volume of 36.8% from 2013 to 2050. Moreover, the effects of land-use changes on flood inundation in Jakarta were much greater than those of land subsidence. The government’s current target to stop land subsidence by 2020 would cause a 7.7% decrease in the flood inundation volume by 2050. Furthermore, controlling and regulating land-use/cover changes by 2020 would cause a 10.9% decrease in the flood inundation volume by 2050. From these results, we conclude that a flood mitigation plan should be made not only for land subsidence, but also for land-use changes.
Twenty-four simulations were carried using the Meteorological Research Institute-Atmospheric General Circulation Model (MRI-AGCM) to predict the late 21st century climate under scenario A1B of the Special Report on Emissions Scenarios. Future climate analogues were identified for Central American capital cities using a recently developed nonparametric method. We used MRI-AGCM3.2H with a horizontal resolution of approximately 60 km, three convection schemes, four sea surface temperature distributions, and two initial conditions. Thus, the total ensemble size was 24, with a simulation period of 25 years. Most of the future analogues are at lower latitudes than their target cities, or near biological diversity and endemism hotspots like coral reefs and mangrove forests. Projected seasonal variations in surface air temperature and rainfall in Panama City were similar to the present-day climate of Soc Trang, located at the mouth of the Mekong River in Vietnam. The nonparametric method introduced in this study for identifying climate analogues can be utilized for impact assessments under a changing climate.
Sediment replenishment is an effective method for resupplying depleted sediment and detaching overgrown algae in the downstream reaches of a dam. In this study, we used empirical data to examine the effects of sediment replenishment on bed material size and algal biomass in the downstream reaches of the Futase Dam, Chichibu City, Saitama Prefecture, Japan. Assuming that algae detach from bed materials when they are moved by water flow, we calculated the tractive force on the riverbed (τ) and allotted a threshold bed material size in motion (Dcri) for each given τ. The resulting bed material in the downstream reaches of the dam in any year was typically finer than that in the previous year when flooding in the rainy season transported a large volume of sediment. Algal biomass was lower when monthly Dcri exceeded 2 mm, versus when it was less than 2 mm. These results suggest that replenishment of fine bed materials accelerates algal detachment and restricts the accumulation of algal biomass by reducing bed stability.
In this study, we propose a new approach for model validation that can be applied to the projection of possible future storm surge heights (SSHs) on the regional scale. First, this study conducts a series of SSHs for the southeastern coast of the Korean Peninsula (KP) by six typhoons that produced SSHs over 1.0 m since 1979 and identifies the bias between simulated and observed SSHs. Next, formulas for the bias correction using a geographic parameter, in particular the coastline complexity factors, are drawn and validated. Finally, the effect of the proposed bias correction on projection of future SSHs is examined by performing simple tests to consider only central pressure drops to reflect the impact of climate change. It can be seen that the bias correction method considering the coastline complexity can improve the model’s accuracy by 14% to 23% and prevent potential overestimation by up to 20% of the maximum SSHs considering climate change effect on the southeastern coast of the KP.
The authors developed a methodology for identifying dominant runoff mechanisms of a watershed and their lumped modeling as a data-based modeling approach with precipitation and runoff data which would contribute to the reduction of uncertainties in both the model structure and the model parameter. We firstly separated a hydrograph into several runoff components by a recession analysis of runoff data and a filter separation method. Secondly, we estimated storage as a function of runoff for each component. Finally, we constructed a single Tank model for each component, where both the runoff component and the estimated storage were used as constraint conditions in identifying coefficients of runoff and infiltration. By applying this approach, we found that (1) the constructed Tank model perfectly traced the runoff components separated by the filter separation method, (2) there are almost no uncertainties in the model structure and the parameter if the result of filter separation can be assumed to be reliable, and (3) we can even estimate effective rainfall with our approach. These results imply our methodology allows identifying and modeling dominant rainfall-storage-runoff mechanisms with minimal uncertainties in model structure and parameter, using hourly precipitation and runoff data alone.
This paper aims to evaluate the effect of mixed-cropping of rice and upland crops on evapotranspiration (ET) in a small seasonal wetland in the north-central Namibia. Meteorological observations were conducted in the experimental sloped field, which simulated the cultivation of both rice in a wetland environment and upland crops in the surrounding rain-fed area, and included a reference wetland with natural vegetation. During cultivation, ET from the rice field was similar to that from the wetland. However, during the dry period ET was remarkably reduced in the post-harvest field, while continuous ET occurred in the natural wetland even after surface water had dried up. The response of surface conductance to meteorological variables was investigated by means of the Jarvis–Stewart conductance model. During cultivation, surface conductance of the rice field and the wetland had a distinct stress response compared with that of the rain–fed crop field. During the dry period, surface conductance of the wetland site, in which the surface water dried–up, still responded to the meteorological conditions in contrast to those of the post-harvest field with plowed bare soil.