Nilendu Singh

The extreme rainfall event during June 2013 in the Western Himalayas caused widespread flash floods, which triggered landslides, a lake-outburst, and debris flow. For the hydrological study of such an unexpected extreme event, it is essential to have reliable and accurate rainfall predictions based on satellite observations. The mountainous state of Uttarakhand is covered by complex topography, and this state has few, unevenly distributed, rain gauge networks. This unique study was conducted to evaluate three satellite based rainfall products (i.e., TMPA-3B42, Global Satellite Mapping of Precipitation (GSMaP), and NOAA CPC Morphing Technique (CMORPH)) against the observed rain gauge-based India Meteorological Department (IMD) gridded dataset for this rainfall episode. The results from this comprehensive study confirmed that the magnitude of precipitation and peak rainfall intensity were underestimated in TMPA-3B42 and CMORPH against gauge-based IMD data, while GSMaP showed dual trends with under-and over-predictions. From the results of the statistical approach on the determination of error statistic metrics (MAE (mean absolute error), NRMSE (normalized root mean square error), PBIAS (percent bias), and NSE (Nash-Sutcliffe efficiency)) of respective satellite products, it was revealed that TMPA-3B42 predictions were more relevant and accurate compared to predictions from the other two satellite products for this major event. The TMPA-3B42-based rainfall was negatively biased by 18%. Despite these caveats, this study concludes that TMPA-3B42 rainfall was useful for monitoring extreme rainfall event in the region, where rain-gauges are sparse.

ABSTRACT The regional impacts of future climate changes are principally driven by changes in energy fluxes. In this study, measurements on micrometeorological and biophysical variables along with surface energy exchange were made over a coniferous subtropical chir pine (Pinus roxburghii) plantation ecosystem at Forest Research Institute, Doon valley, India. The energy balance components were analyzed for the two years to understand the variability of surface energy fluxes, their drivers and closure pattern. The period covered two growth cycles of pine in the years 2010 and 2011 without and with understory growth. Net shortwave and longwave radiative fluxes substantially varied with cloud dynamics, season, rainfall induced surface wetness and green growth. The study clearly brought out the intimate link of albedo dynamics in chir pine system with dynamics of leaf area index (LAI), soil moisture and changes in understory background. Rainfall was found to have tight linear coupling with latent heat fluxes. Latent heat flux during monsoon period was found to be higher in higher rainfall year (2010) than low rainfall year (2011). Higher or lower pre-monsoon sensible heat fluxes were succeeded by noticeably higher or lower monsoon rainfall respectively. Proportion of latent heat flux to net radiation typically followed the growth curve of green vegetation fraction but with time lag. The analysis of energy balance closure (EBC) showed that the residual energy varied largely within ±30% of net available energy and the non-closure periods were marked by higher rainspells or forced clearance of understory growths.

A coupled ecophysiological and micrometeorological study was carried out in young pine (Pinus roxburghii) plantation at Forest Research Institute, Dehradun to ascertain seasonal carbon fluxes behavior and its environmental controls. The results showed that seasonality of Leaf Area Index (LAI) and its ambient subtropical climatic condition played very important role in seasonal carbon accumulation trend in addition to land management practices. The mean annual net primary productivity stands -2 -1 -1 -1 at 1.57 g C m day (5.75 t C ha yr) with distinct phenophasic and seasonal variations. Mean annual light use efficiency was -1 2.33 gMJ , with prominent peak in postmonsoon season. The normal trend of carbon fluxes varied from source to sink mode in the annual cycle. The LAI of physiologically dormant plants decreased during winter with net carbon assimilation being negative, i.e. it respired more than net photosynthetic uptake. Present study also brought out the role of understorey in...

ABSTRACT The carbon and water fluxes are key aspects of ecosystem functions. Their coupling processes are complicated over terrestrial ecosystems. To understand the seasonal dynamics and coupling mechanism between these fluxes in deciduous subtropical coniferous vegetation in the western Himalayas, the present study involved systematic and concurrent measurements of micrometeorological variables and ecophysiological characteristics within a uniformly distributed young pine forest ecosystem at Forest Research Institute, India. Micrometeorological data were measured continuously for a 14-month period along with key ecophysiological measurements during a growth cycle (2010-2011). These measurements allowed an examination of daytime net canopy assimilation (Cnar), evapotranspiration (ET), light use efficiency (LUE), and water use efficiency (WUE) of this coniferous ecosystem. Results showed that daily variations of ET, Cnar, LUE and WUE were strong functions of temperature and vapour pressure deficit (VPD) but within optimal limits, while these efficiency terms had a close relationship with LAI dynamics and phenology on the seasonal scale. ET being the principal component of water balance (~50% of rainfall), varied between 0.7 and 4.2 mm d-1 depending on LAI and seasonal cycle. It was primarily driven by evaporative demand (VPD) (R2 = 0.696, P < 0.001) and air temperature (R2 = 0.92, P < 0.001) in addition to radiation and PAR. Significant and stronger correlation of ET against VPD as compared to soil water content (R2 = 0.35) in pine ecosystem is indicative of dominant role of stomatal control. The seasonal course of Cnar (peak in post-monsoon and minimum during winter) followed the LAI dynamics except during monsoon. The Cnar of pine varied between 1.2 and 10.5 µmol CO2 m-2 s-1 while that of understory (Lantana camara) varied between 3.7 to 17.3 µmol CO2 m-2 s-1. Pooled data over the seasons showed significant linear relation between Cnar and ET or evaporative fraction. The degree of coupling between water and carbon exchange was strongest in the post-monsoon and spring seasons, and weaker during winter and monsoon seasons. A remarkable strong link between resource use efficiencies (WUE and LUE) was observed particularly in the dry season. This study highlights specifically the response of carbon and water exchange to environmental conditions that would help in forest management by optimizing water resource use. The optimal mix of resource use efficiencies may be the ecophysiological reason of pine ingression into higher reaches of oak forests in the western Himalaya.

ABSTRACT The regional impacts of future climate changes are principally driven by changes in energy fluxes. In this study, measurements on micrometeorological and biophysical variables along with surface energy exchange were made over a coniferous subtropical chir pine (Pinus roxburghii) plantation ecosystem at Forest Research Institute, Doon valley, India. The energy balance components were analyzed for the two years to understand the variability of surface energy fluxes, their drivers and closure pattern. The period covered two growth cycles of pine in the years 2010 and 2011 without and with understory growth. Net shortwave and longwave radiative fluxes substantially varied with cloud dynamics, season, rainfall induced surface wetness and green growth. The study clearly brought out the intimate link of albedo dynamics in chir pine system with dynamics of leaf area index (LAI), soil moisture and changes in understory background. Rainfall was found to have tight linear coupling with latent heat fluxes. Latent heat flux during monsoon period was found to be higher in higher rainfall year (2010) than low rainfall year (2011). Higher or lower pre-monsoon sensible heat fluxes were succeeded by noticeably higher or lower monsoon rainfall respectively. Proportion of latent heat flux to net radiation typically followed the growth curve of green vegetation fraction but with time lag. The analysis of energy balance closure (EBC) showed that the residual energy varied largely within ±30% of net available energy and the non-closure periods were marked by higher rainspells or forced clearance of understory growths.