Comparative observation and estimation of precipitation and dew/frost on the Northeastern Tibetan Plateau

Based on the understanding of long-term field observations, we monitored the amount of precipitation and dew/frost with field experimental studying in mountainous catchment, using the precipitation observation network in alpine mountainous regions and independently designed observation methods for dew and frost. The purposes of field experiments were to quantitatively identify the distribution pattern of precipitation and dew/frost, characterize the vertical water inputs in catchment scale, and further analyze the formation and transformation law of water resources in inland river source regions.  This dissertation also aimed to rationally develop and utilize precipitation and dew/frost resources, and identify the relationship between precipitation and dew/frost in alpine ecosystems, which will provide the perspective and knowledge of cold region hydrology for promoting regional sustainable development. The main conclusions of the dissertation are as follows:

(1) the relationships between dew/frost and precipitation, and dew/frost and evaporation in the alpine steppe of Hulu catchment.

The interannual ranges in the alpine steppe of Hulu catchment was from 32.36 to 59.68 mm for dew/frost formation, from 404.1 to 557.9 mm for the precipitation and from 343.9 to 372.0 mm for the evaporation.  Therefore, the amount of dew/frost accounts for 5.7% to 12.7% of the precipitation and 7.2% to 17.4% of the evaporation in the same period.

(2) Dew/frost had a significant impact on eco-hydrological system in dry season and comparatively high percentage of frost.

In the dry season, averaged amount of multi-year dew/frost accounted for 54.5% and 40.9% of the multi-year mean precipitation and multi-year mean evapotranspiration, respectively.  Therefore, dew/frost mostly occurred in the dry season.  The annual mean dew amount was 5.90 mm, and the annual mean amount in the dew proportion of dew/frost was 15.26%, while the annual mean frost amount was 31.33 mm, and the frost proportion in dew/frost was 84.74%.  On the monthly scale, frost was mainly generated from March to May and from September to November, which corresponded to the stages of freezing-thawing and thawing-freezing, respectively.

(3) dew/frost events highly depending on precipitation events based on isotope results.

Stable isotope of atmospheric precipitation in the Hulu catchment changed between each season which was noticeable from May to September; not obvious from October to April of the following year.  The spatial and temporal distribution patterns of δ18O and δD isotopes were mainly influenced by the sources of water vapor and small-scale environment.  The occurrence of dew/frost often occurred a few days after a precipitation event, and its stable isotope composition and its variation law were consistent with that of precipitation.  The results showed that the formation and source of dew/frost water are highly dependent on the occurrence of precipitation.  Dew had similar characteristics of precipitation occurred earlier.  However, frost mainly happened in the freezing-thawing process of soil, and is closely related to the isotope value of soil vegetation, which needed further analysis of soil and vegetation isotope samples.