摘要：山地流域は水の供給源であり，水収支の把握は水資源管理の観点から重要だが，標高の高い地域では観測が容易でないため情報が限られている.本研究では山地帯林と亜高山帯林からなる秩父山地の川又流域（標高628～2,475 m，流域面積94 km2）の水収支を求める.対象流域は面積が大きいため，降水の空間分布を考慮する必要がある.そこでまずは流域内外の地上雨量計による観測値を用いてレーダー雨量計による1 kmメッシュ解析雨量の精度検証を行い，月降水量，年降水量とも解析雨量は地上雨量計による観測値とほぼ1：1の対応関係があることを確認した.次に解析雨量を用いて流域平均降水量をもとめ，流出量の観測値とあわせて2009～2018年の年水収支を得た.平均すると年降水量1,747±245 mm y－1，年流出量1,375±220 mm y－1，年損失量が372±78 mm y－1であった.年損失量はほぼ年蒸発散量に等しいとすると，川又流域の年蒸発散量は，同じ関東地方の標高の低い流域と比べて数百ミリ小さいこと，また緯度の高い北海道や東北地方にある冷温帯林や亜寒帯林からなる流域と同程度であることが示唆された.
其他摘要：Mountains are a source of water; thus information about water balance is important for water resources management. However, there is a lack of information, especially for high elevation areas, because it is often difficult to conduct measurement in high elevations. Here we report water balance at Kawamata catchment in the Chichibu Mountains (elevation 628-2,475 m, catchment area 94 km2) that consist of montane and subalpine forest. Because this catchment is relatively large, we need to consider spatial variation in precipitation. We tested the accuracy of 1 km mesh radar-raingauge analyzed precipitation, using measured point precipitation data within and near the Kawamata catchment and found that both monthly and annual precipitation measured by radar-raingauge and tipping bucket rain gauges showed almost 1:1 correspondence. We calculated water balance for years 2009-2018 using catchment mean annual precipitation obtained by 1 km mesh radar-raingauge analyzed precipitation and measured annual discharge. On average, annual precipitation, discharge and loss were 1,747±245 mm y－1, 1,375±220 mm y－1 and 372±78 mm y－1, respectively. This annual loss was considered equal to the annual evapotranspiration at Kawamata catchment. Our data and previous reports suggest that even in forested catchment in the same Kanto Region, annual evapotranspiration in a higher elevation catchment covered with montane and subalpine forest can be a few hundred millimeters smaller than that of forested catchment in a low mountain range and is also comparable to that of cool temperate and subalpine forests in the higher latitudes, such as Hokkaido and the Tohoku region.
关键词：水収支;解析雨量;山地森林流域;流域平均降水量;蒸発散量
其他关键词：Water Balance##Radar-raingauge analyzed precipitation##mountain catchment##catchment mean precipitation##evapotranspiration
