Spatial and Temporal Variability of Atmospheric Hg in North-Western and Central Europe-Observations on Different Time Scale

Abstract. Hydrological models for runoff estimations and flash-flood predictions are very sensitive to rainfall's spatial and temporal variability. The increasing use of radar and satellite data in hydrological applications, due to the sparse distribution of rain gauges over most catchments worldwide, requires improving our knowledge of the uncertainties of these data. In 2011, a new super-dense network of rain gauges, containing 27 gauges covering an area of about 4 km2, was installed near Kibbutz Galed in northern Israel. This network was established for a detailed exploration of the uncertainties and errors regarding rainfall variability in remote-sensing at subpixel-scale resolution. In this paper, we present the analysis of the first year's record collected from this network and from the Shacham weather radar. The gauge–rainfall spatial correlation and uncertainty were examined along with the estimated radar error. The zero-distance correlation between rain gauges was high (0.92 on the 1-min scale) and increased as the time scale increased. The variance of the differences between radar pixel rainfall and averaged point rainfall (the variance reduction factor – VRF) was 1.6%, as measured for the 1-min scale. It was also found that at least four uniformly distributed rain stations are needed to represent the rainfall on the radar pixel scale. The radar–rain gauge error was mainly derived from radar estimation errors as the gauge sampling error contributed up to 22% to the total error. The radar rainfall estimations improved with increasing time scale and the radar-to-true rainfall ratio decreased with increasing time scale. Rainfall measurements collected with this network of rain gauges in the coming years will be used for further examination of rainfall's spatial and temporal variability.

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Implications for water cycle dynamics in the Upper Jhelum River Basin of North-Western Himalayas based on hydrogen and oxygen isotope signatures of precipitation, surface water, and groundwater

10.5194/egusphere-egu21-1077 ◽

2021 ◽

Author(s):

Tanveer Dar ◽

Nachiketa Rai ◽

Sudhir Kumar

Keyword(s):

Surface Water ◽

Stable Isotope ◽

Isotopic Composition ◽

Lake Water ◽

Temporal Variability ◽

Himalayan Region ◽

Spatial And Temporal Variability ◽

Jhelum River ◽

Jhelum River Basin ◽

North Western

We have used stable isotopes of oxygen and hydrogen (&#948;18O and &#948;D) which are important tracers for understanding various hydrological processes, to assess the spatial and temporal variability due to dual moisture sources in the Upper Jhelum River Basin (UJRB) of the north-western Himalayan region. The HYSPLIT back trajectory analysis shows large variability in spatial moisture transport pathways over the region during Southwest monsoon (SWM) and is mainly restricted to the Mediterranean Sea during Western disturbances (WDs). The isotopic composition of precipitation is significantly controlled by temperature and Relative Humidity during precipitation events from WDs; however, this control is found to be weak during the SWM.Stable isotope signatures of precipitation are found to show a well-defined altitudinal effect (&#948;18O=0.19&#8240;/100m) and a negative correlation with ambient temperature (R&#178; = 0.65, p<0.01 for WDs & R&#178;=0.48, p>0.1 for SWM). Mixing various tributary waters with different isotopic compositions leads to variability in the Jhelum River&#8217;s (JR) isotopic composition along its course. The observed spatial variability of &#948;18O and d-excess results from the exchange processes between groundwater and surface water. The higher depletion of precipitation during WDs leads to depletion of surface and groundwater and produces enrichment due to the evaporative loss of heavier isotopes due to drier weather conditions during SWM. Evaporation signals are more prominent in shallow groundwater (SGW) and lake water, indicating SGW being discharged in the proximity of lake water bodies. The isotopic values in the upper reaches are observed to be depleted, potentially due to inputs from melting glaciers and snow. In the middle, it reaches slightly enriched, likely due to shifts in groundwater and rainfall inputs. In the downstream, due to increased residence time and flat topography, the isotopic composition is relatively enriched, potentially related to the evaporative losses of heavier isotopes. The d-excess values in UJRB are found to vary between 11&#8240; to 20&#8240; with an average value of ~17&#8240;, which is relatively higher than the long-term average observed for the Indian summer monsoon (~8&#8240;), and Upper Indus in the Ladakh region (11.7&#8240;) but almost similar to observed for Lower Indus (18&#8240;).The contribution of moisture from each source (WDs and SWM) are estimated using a two-component mixing model. The moisture source contribution over UJRB via WDs is 75%(&#177;20) from the Mediterranean Sea and 20%(&#177;10) from SWM. WDs contribution over UJRB is higher than in the Trans-Himalayan region in the Ladakh (Indian sector in the east) but smaller in Lower Indus Basin (Pakistan sector in the west). Hence, the influence of moisture of WDs decreases from west to east along the Himalayan region. This work based on stable isotope geochemistry of oxygen and hydrogen highlights the effects of meteorological and physiographic controls on the moisture dynamics and contributes to explain the spatial and temporal variability of hydrologic processes in the region.

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