Shunji Ohta

Probable effects of CO2-induced climatic changes on net primary productivity of terrestrial vegetation in East Asia

Changes in the net primary productivity (NPP) of natural vegetation of monsoon East Asia were simulated under three, doubled CO2-climate scenarios (GISS, GFDL and UKMO). These three scenarios and baseline climate data were converted to grids of 1o×1o meshes. The gridded climatic data were used together with the Chikugo model to assess NPP under baseline and CO2-doubling climates. The potential total net production (TNP0) of East Asia was climatically evaluated to be 154×108 t dry matter year−1. The climatic changes induced by a doubled CO2 concentration are predicted to increase the TNP0 by approximately 9–15%, depending on the climatic scenario. The estimated increase in TNP0 would be limited by the difference between the rate of shift of climatic zones and the rate of migration of vegetation formations.

Probable effects of CO2-induced climatic warming on the thermal environment of ponded shallow water

A physical model was developed for describing the thermal environment of ponded shallow water as a model for rice fields in relation to climatic conditions. The model was used to assess probable effects of CO2-induced warming on the thermal conditions of ponded shallow water. It was assumed that an altered equilibrium climate was produced by atmospheric CO2 which was twice that of present levels. The 1951–80 climatic means of Japan were used as baseline data. Water temperature and energy balance characteristics predicted from the model were compared between both climates. The most notable results were that water temperature under CO2 doubling rose 2 to 4 °C. These increases in temperature would induce a remarkable northward shift of the 15 °C isotherm which characterizes the isochrone of safe transplanting dates for rice seedlings. CO2-warming would have a considerable influence on the energy balance characteristics, intensifying the evaporation rate from the water surface. Changes in thermal conditions of rice fields due to CO2-induced climatic warming are, therefore, expected to bring about significant effects on aquatic environments and the life forms they support.

Climatic Change Scenarios for Monsoon Asia Based on 2 × CO2-GCM Experiments

This investigation is made of the possible climatic change scenarios due to a doubling of carbon dioxide concentration in the atmosphere. The three global climate or general circulation models(GCM) have been used to produce the climatic change scenarios for Monsoon Asia. Using these scenarios, the information was obtained on the possible distribution of annual air temperature, annual precipitation, annual global solar radiation, annual net radiation, and annual average of radiative dryness index on the Monsoon Asia. Regional averages of relative changes in climatic elements under 2xCO2 induced warm climates were calculated for the four sub-areas corresponding to the ice and desert climate area(I), cool and/or warm temperate climate area (II), subtropical and/or tropical climate area(III), and humid tropical area (IV). The relative changes in annual temperature were fairly large on the sub-area I than on the other sub-areas. The grid mesh maps showing the regional distribution of climatic elements under 2xCO2 conditions can be used approximately as climatic change scenarios for Monsoon Asia.

Modeling the spatio-temporal distribution of the Anopheles mosquito based on life history and surface water conditions

To describe the temporal and geographic distribution of the malaria vector mosquito (Anopheles) at a fine resolution, we modeled the relationship between mosquito life history and climate conditions, focusing on temperature- dependent development of the mosquito. Because Anopheles has aquatic immature life stages, the model was designed to incorporate information on surface moisture conditions suitable for the mosquito. Development was estimated using either air or water temperature, depending on the developmental stage. The model was able to predict seasonal patterns of occurrence of Anopheles at representative sites with reasonable accuracy. Individual emergence of mosquitoes was limited by low water temperatures and/or low moisture conditions at the soil surface in cold or dry seasons. This model was then applied to obtain the geographic distribution of Anopheles occurrence in Monsoon Asia. Spatio-temporal emergence of the Anopheles mosquito was successfully represented using the model and simple climate data. This model can be used to predict the distribution of the mosquito for malaria risk assessments under future scenarios involving climate change and the effects of El Nino-Southern Oscillation events.

Effect of 2 x CO2 climatic warming on water temperature and agricultural potential in China

Water temperature under the current and future climates are estimated using the water temperature physical model, weather data and general circulation model (GCM)- scenarios to assess effects of C02-induced climatic changes on the natural environment surrounding the agriculture of China. The most notable results obtained for the GCM-2 X CO2 scenarios are that the safe transplanting date for rice plants would be about 20-30 days earlier than that under present climatic conditions. This means that the rice cultivation period would be prolonged by approximately 30-50 days, and also that the increase in effective accumulated water temperature is more than 700-1200 degree days in the semi-arid region of China and 1300-2000 degree days in main rice-producing areas of the southern part of China. This indicates that the northern limit of the safely cultivable area of Indica and hybrid rice cultivars may reach on the south of Huang He, indicating the increment in the potential rice production of China. On the other hand, these changes in temperature environment of shallow water due to C02-climate warming could cause an increase in evaporation from water surface. The increase in evaporation due to the future climatic warming is about 16-40%. However, the GCM-2 X CO2 scenarios indicate that the mean increasing rate of precipitation due to climatic change would be only 15-20% by the middle of the 21st century. Therefore, the imbalance of water to be expected in the next century may cause a shortage of water resources available for paddy rice cultivation.

Ecophysiological and Climatological Effects on Distribution of Vector Species and Malaria Incidence in India

The magnitude of regional malaria risk is dependent primarily on the dynamics and distribution of the vector species, which are determined mainly by climate conditions. A coupled model with ecophysiological and climatological factors was developed to estimate the spatiotemporal distribution of the five species of dominant malaria vectors in monsoon Asia. Here, we examined how the potential distribution obtained from the model could explain trends in malaria incidence observed in India, which has the highest number of confirmed cases of malaria in Asia. Most notably, there was a significant positive correlation between annual malaria incidences and the maximum generation number of vectors for each state (p < 0.001). Malaria incidence tended to increase exponentially as vector generation number increased. In addition, the interannual variation in observed regional malaria incidences was synchronized with that of the potential number of vector generations. The observed seasonal peak of malaria incidences corresponded closely to the simulated appearance period of vector species, except for intensively irrigated areas that experience anthropogenic impacts on hydrologic conditions. Simulated vector distributions effectively expressed spatial and temporal prevalence of malaria in India. This novel approach to modeling based on vector ecology is an effective method for assessing malaria risk.

Effect of irrigation systems on temporal distribution of malaria vectors in semi-arid regions

Previous research models have used climate data to explain habitat conditions of Anopheles mosquitoes transmitting malaria parasites. Although they can estimate mosquito populations with sufficient accuracy in many areas, observational data show that there is a tendency to underestimate the active growth and reproduction period of mosquitoes in semi-arid agricultural regions. In this study, a new, modified model that includes irrigation as a factor was developed to predict the active growing period of mosquitoes more precisely than the base model for ecophysiological and climatological distribution of mosquito generations (ECD-mg). Five sites with complete sets of observational data were selected in semi-arid regions of India for the comparison. The active growing period of mosquitoes determined from the modified ECD-mg model that incorporated the irrigation factor was in agreement with the observational data, whereas the active growing period was underestimated by the previous ECD-mg model that did not incorporate irrigation. This suggests that anthropogenic changes in the water supply due to extensive irrigation can encourage the growth of Anopheles mosquitoes through the alteration of the natural water balance in their habitat. In addition, it was found that the irrigation systems not only enable the active growth of mosquitoes in dry seasons but also play an important role in stabilizing the growth in rainy seasons. Consequently, the irrigation systems could lengthen the annual growing period of Anopheles mosquitoes and increase the maximum generation number of mosquitoes in semi-arid subtropical regions.

Possible Effects of Future Climate Changes on the Maximum Number of Generations of Anopheles in Monsoon Asia

The predicted increase in global temperatures is expected to affect ecosystem, human health and society. In particular, a longer growing period due to climate warming is expected to enhance the growth and reproduction of some kinds of organisms (Kiritani, 2006; Ohta & Kimura, 2007). Northern and altitudinal shifts in vector species that cause infectious diseases have been observed worldwide (Barker & Lindsay, 2000; Hales et al., 2002). Conversely, the endemicity of vector-borne diseases such as malaria has decreased during the past century (Gething et al., 2010). The reason for this decrease is the economic development and disease control during this period (Hay et al., 2009; Gething et al., 2010). However, the recession of malaria during the last century did not correspond to a reduction in the ranges of vector species. Because of the complex relationship between malaria and climate (Martin & Lefebvre, 1995), the potential distribution of vectors and climate conditions of their habitats without human interference need to be elucidated. Malaria is the chief disease caused by vectors breeding on shallow surface waters. Because survival and reproduction rates of mosquitoes are mainly determined by the temperature and humidity of their habitats, climate factors determine whether a location is suitable for the transmission of a wide range of infectious diseases. Projected changes in temperatures and the hydrological cycle will cause changes in the geographical distributions and population dynamics of vectors, thus altering the patterns of infectious disease transmission (Martin & Lefebvre, 1995; Martens et al., 1999). In particular, one of the most interesting aspects is how climate change could affect the geographical distributions and incidence patterns of the diseases caused by mosquitoes. However, most investigators assessing the impacts of climate change on the incidence and geographical range of malaria assume that mosquito distribution would not change under future climate conditions (Martens et al., 1999; van Lieshout et al., 2004). These investigators assessed the risk of malaria transmission based on the geographical distribution of particular mosquito species by country or administrative unit (World Health Organization, 1989; Jetten & Takken, 1994). However, mosquitoes are not always uniformly distributed within a country, and their range typically crosses national borders (Kashiwada & Ohta, 2010). Martin & Lefebvre (1995) developed the Malaria Potential Occurrence Zone model,

Probable Effects of Climatic Changes on Plant Production of Monsoon Asia

This paper attempts to estimate the geographical distribution of net primary productivity (t dry matter/(ha · yr)) of natural vegetation in Monsoon Asia, in which about 45% of the world population is living at present. Estimates have also been made of probable effects of climatic changes to be induced by CO2 increase and human land use on the total net primary production (t dry matter/yr) of this area. The Chikugo model based on relationship between climatic factors and dry matter production was used to calculate NPP values of natural vegetation. Normal climate data and climate scenarios generated by three GCMs were used to estimate to what extent plant production is affected by climatic changes due to doubled CO2. It was expected that the potential total net production of this area will increase by about 10% than the present level. This implies that the potential of this area for agriculture, animal production and forestry would increase consequently with the climatic changes. To make clear probable effects of human land use on the plant production, the data on land use of the Republic of Indonesia were used in cooperation with the Chikugo model. It was predicted that the actual total net production of this country is about 88% of its potential one.

Spatial Patterns of Anthropogenic Carbon Emission and Terrestrial Net Productivity

This paper describes the current spatial patterns of the net primary productivity (NPP) of the terrestrial vegetation and carbon emission (C) in the world due to the burning of fossil fuels in order to clarify the amount of expansion of human activity. The C/NPP value varies spatially from almost zero to several tens of thousand times the local NPP. C/NPP is higher under the condition of extensive human activities due to a high human population density or when the local NPP is extremely low in severe climatic zones. In contrast, the low C/NPP areas are distributed mainly in sparsely populated districts, loading to a low impact of human activity. Although the area where C/NPP is less than 10% accounts for about 70% of the entire land area, one-third of these areas cannot contribute to carbon absorption because of low NPP with a shortage of climatic resources. Since more than half of the areas of the remaining areas are agricultural land and forest ecosystems with high NPP, the possible afforestation area was evaluated to be maximum of ; here only sequestrate carbons that correspond to 2% of the global total NPP are present. These analyses revealed that presently most of the areas where the NPP is high are those exclusively used by humans and that it is difficult for large-scale forest plantations to absorb a substantial amount of the carbon emitted annually by humans.