A comparison of the baseflow recession constant (K) between a Japanese cypress and mixed-broadleaf forest via six estimation methods

The baseflow recession constant (K) is known to be a versatile parameter used in forecasting low flows, flow-frequency analyses, improving regional models, and other various hydrological analyses. This study took place in Inuyama city, Aichi prefecture, central Japan, where K for two catchments of differing vegetation [Japanese cypress (CF), 2.42 ha; mixed-broadleaf (MB), 2.08 ha] were produced via six estimation methods and compared. Water level was recorded by dataloggers (converted to daily discharge) and rainfall, by raingauges. Over 5 years (May 2013–April 2018), 18 baseflow recession events were qualified for analysis from which K were calculated. Overall, K in CF (0.969) was marginally higher than in MB (0.955), which translates to lower water depletion in CF possibly due to lower transpiration. In each catchment, K did not differ significantly between the growth and dormant period. Root mean square error (RMSE) is lower and less variable in CF than in MB. Reproducing baseflow using season-specific K values did not show any clear reduction in RMSE; hence, the complexity is not justified. In general, all K-estimators performed well (low RMSE) and can be used. Out of six K-estimators, two have relatively higher standard deviation (SD) and will underestimate baseflow especially when the K was produced from short (< 6 days) baseflow recession limbs. Others reproduce unbiased baseflow but have relatively higher SD and RMSE. None of the estimators were unusable, but two estimators that have the lowest SD and least bias were recommended

A comparison of hydrological characteristics between a cypress and mixed-broadleaf forest: Implication on water resource and floods

Broadleaf or conifer forest? – an ongoing dilemma as regards water resource and flood prevention. Although conifer trees use less water and are hydrophobic, existing studies at the watershed scale have shown varying results due to variability in meteorological conditions and forestry practices. In this study, two adjacent headwater catchments [2.42 ha cypress (CF); 2.08 ha mixed broadleaf (MB)] were gauged. The study area in central Japan has a warm temperate climate with high annual rainfall and typhoons. Daily discharge (n = 1398) and storm event hydrographs (n = 242) were compared between CF and MB and discussed in light of water availability and storm event runoff characteristics. Overall water yield in CF was 6.4% lower than in MB but this was caused by lower streamflow on high discharge periods (30% frequency); thus, may not adversely affect municipal/agricultural water supply. For 70% of the time including during dry periods, water yield was higher in CF. This agrees with the principle that conifers use less water than broadleaf trees – even at the forested catchment scale. Discharge in the CF stream is also less variable than that in the MB stream. During storm events, the CF stream has higher flashiness (shorter response time to rainfall and higher peak discharge) than the MB stream; but in larger storms (≳70 mm), the MB stream may have higher peak discharge. Our data demonstrates that a well-managed plantation forest does not necessarily have inferior hydrological function compared to a natural broadleaf forest, which differs from the stereotype. Frequencies of high and low flows as well as runoff characteristics were also presented in hopes of promoting better forestry decisions when considering water demand and existing stormwater drainage infrastructures

Climate classification of Asian university forests under current and future climate

Species diversity and the distribution of forests are closely related to climate, and climate classifications have been used to characterize vegetation distribution for over a century at the global scale. In contrast, climate type and dominant forest species may not be accurately classified at the forestry stand scale due to limited observational data and the influence of terrain. The collaboration of Asian university forests traverses 37.4° of latitude, from Hokkaido in Japan to Sabah in Malaysia. This study used both long-term observations and Worldclim 1-km resolution gridded datasets to classify well-managed Asian university forests according to the Trewartha climate classification method. Outputs from circulation models of the Coupled Model Inter-comparison Project Phase 5 (CMIP5) were then used to assess projected changes in future climate. Results showed that the current climate subtypes of the Asian university forests were consistent between the observations and Worldclim database. Ensemble projections of future climate suggested two likely drastic forest changes under a moderate emissions scenario during 2041–2060; parts of the Seoul National University Forests are likely to shift from a temperate to a subtropical climate, while sections of forests in Thailand are likely to shift from a subtropical to a tropical climate

Rainfall Characteristics in a Tropical Montane Cloud Forest, Gunung Alab, Crocker Range Park, Sabah, Malaysia

Generally, the tropical montane cloud forest (TMCF) has known to be the headwater for rivers which are the vital source of freshwater for the downstream user. Though one of the important information for freshwater management is the rainfall characteristics, for TMCF catchment it is still less explored in Sabah. This paper investigates the temporal pattern and variability of rainfall in Gunung Alab experimental catchment (GAEC) in the Crocker Range Park (CRP), Sabah, Malaysia. The analyses were based on rainfall observation data obtained in January 2006 to December 2018. As a comparison, similar analyses were also conducted to the rainfall observation data from a meteorological station in the west coast area of Sabah referred in this study as the coastal area of Kota Kinabalu (CAKK). The average annual rainfall for the 13 years data was 3527.1 mm and 2824.8 mm in GAEC and CAKK, respectively. The yearly average rain days in GAEC was 223 days and in CAKK was 157.1 days. Both stations received maximum monthly rainfall during the intermonsoon season which generally occurred in April - May and September - October. In general, GAEC experienced low intensity of rains in long-duration whereas, CAKK experienced more extreme rainfall (average 2.4 ± 1.9 day yr-1 ) compared to GAEC (0.3 ± 0.9 days yr-1 ). Based on the set of rainfall data, total rainfall of 129.4 mm day-1 and 224.6 mm day-1 can be expected to be equal or exceeded once in 26 years at a probability of 3.85%, in GAEC and CAKK, respectively. In GAEC, one, two, five and ten years of recurrence interval, the expected maximum daily rainfall was estimated at 65.2 mm day-1 , 80.7 mm day-1 , 99.9 mm day -1 , and 114.1 mm day-1 . Whereas, in CAKK, the one, two, five and ten years of recurrence interval of maximum rainfall can be expected at 77.2 mm day-1 , 136 mm day-1 , 168.5 mm day-1 and 196.7 mm day-1 , respectively. The El Niño episodes reduce 10.5 % - 18 % and 2.7% - 27.9% of annual rainfall from the long-term average in GAEC and CAKK. These findings give insight into the potential capacity of GAEC as headwater catchment and reflect the sensitivity of the local rainfall distribution influenced by natural phenomenon namely, the El Niño-Southern Oscillation (ENSO) within the observation period

Enhancing Overland Flow Infiltration through Sustainable Well-Managed Thinning: Contour-Aligned Felled Log Placement in a Chamaecyparis obtusa Plantation

Contour felling is a restoration method used to decrease overland flow (OF) and soil erosion in the world. However, the impact of thinning and the placement of felled logs on OF remains inconclusive. Low ground cover and soil permeability promote OF in Chamaecyparis obtusa (Siebold et Zucc.) Endl plantations, making thinning a method for reducing runoff. We examined the relationship between OF and ground cover in a C. obtusa plantation in Japan. Event-based runoff was monitored in three plots from 2016 to 2021, with 40% thinning conducted in 2019. In plot T1, logs were randomly scattered, and, in T2, logs followed contour lines, while control plots stayed the same. After thinning, both treatment plots showed lower OF than the control plot. The ANCOVA test shows a significant slope reduction in treatment plots compared to the control plot from pre-thinning to post-thinning (T1: 0.67 to 0.26, T2: 0.66 to 0.12, p < 0.001, Tukey HSD test). However, in plot T2, OF remained stable for two years post-thinning, affirming the enduring effectiveness of contour-aligned log placement. This study backs the notion that aligning fallen logs with contour lines boosts long-term OF infiltration, supporting sustainable forest and soil management

Higher Water Yield but No Evidence of Higher Flashiness in Tropical Montane Cloud Forest (TMCF) Headwater Streams

There have been conflicting findings on hydrological dynamics in tropical montane cloud forests (TMCFs)—attributed to differences in climate, altitude, topography, and vegetation. We contribute another observation-based comparison between a TMCF (8.53 ha; 1906 m.a.s.l.) and a tropical lowland rainforest (TLRF) (5.33 ha; 484 m.a.s.l.) catchment in equatorial Sabah, Malaysian Borneo. In each catchment, a 90◦ v-notch weir was established at the stream’s outlet and instrumented with a water-level datalogger that records data at 10-min intervals (converted to discharge). A nearby meteorological station records rainfall at the same 10-min intervals via a tipping bucket rain gauge connected to a datalogger. Over five years, 91 and 73 storm hydrographs from a TMCF and a TLRF, respectively, were extracted and compared. Various hydrograph metrices relating to discharge and flashiness were compared between the TMCF and TLRF while controlling for event rainfall, rainfall intensity, and antecedent moisture. Compared to the TLRF, storm-event runoff in the TMCF was up to 169% higher, reflecting the saturated conditions and tendency for direct runoff. Instantaneous peak discharge was also higher (up to 6.6x higher) in the TMCF. However, despite high moisture and steep topography, stream responsiveness towards rainfall input was lower in the TMCF, which we hypothesise was due to its wide and short catchment dimensions. Baseflow was significantly correlated with API20, API10, and API7. Overall, we found that the TMCF had higher runoff, but higher moisture condition alone may not be sufficient to govern flashiness

Impact of Tunnel Excavation Muck dumped along the canyon on Streamwater Chemistry

岩石中に硫化鉄鉱物を含む岩盤にトンネルを掘削し, 残土を周辺の渓谷に埋め立てると, 硫化鉱物が酸素を含んだ降水や地下水と接触し, 酸化・分解することにより硫酸酸性浸出水が発生し, 生物の斃死や有害金属類の流出などにより周辺環境に悪影響を及ぼす可能性がある。掘削残土の中に酸性化を緩衝する能力を有する鉱物が含まれる場合は, 中和作用により浸出水のpHの低下が抑制されるため, 浸出水のpHは, 硫化鉱物の酸化により生ずる硫酸量と, 緩衝鉱物の分解に消費される硫酸量の兼ね合いによって決まると考えられる。本研究では, トンネル掘削残土の埋め立てによる渓流水の溶存物質濃度の長期的な変化を明らかにするために, トンネル掘削残土の埋め立て区間の直上流, 直下流で, 埋め立て前から後まで23年間, 渓流水質をモニタリングし, その結果に基づき検討した。その結果, 1993～94年に埋め立てが終了した後16年が経過しても, 埋め立てによる渓流水質への影響は続いていた。埋め立て区間の下流ではSO4(2-), Ca(2+), アルカリ度が有意に高い状態が続いているが, 渓流水のpHの低下はみられず, Ca(2+)を主とするカチオンが, S含有鉱物の分解によって生じた硫酸を中和し, pHを中性に保ったと考えられる。埋め立てがCa(2+)以外のカチオン濃度を増加させた期間は3～5年間にとどまり, SiO2には埋め立ての影響がなかった。影響の継続期間については, ワサビ沢では31年, トウバク沢では17年から20年と試算された。To show the long-term changes in streamwater quality after dumping tunnel excavation muck along the canyon, streamwater chemistry monitoring was undertaken at points upstream and downstream from the site where rock muck had been dumped in Wasabi and Toubaku Creek over 23 years. The concentrations of SO4(2-) below the dumping site were significantly increased which is consistent with the results found in the previous study that some of the rock muck contained Greigite. The pH of streamwater below the dumping site was, however, not significantly different from that above the dumping site, suggesting that SO4(2-) was neutralized by some cations such as Ca(2+) which was also significantly increased below the dumping site. Although the difference of mean annual SO4(2-) concentration between the points upstream and downstream of the dumping site became smaller, the difference was still significant for 17 years after dumping. It takes about 31 years in the Wasabi creek and from 17 to 20 years in the Toubaku Creek for the SO4(2-) concentration of streamwater downstream of the rock muck to be returned to the level found upstream

Long-Term Monitoring and Research in Forest Hydrology: Towards Integrated Watershed Management

Forest hydrology, as a discipline, was designed to address fundamental questions regarding the impact of deforestation on floods and droughts [...