Vulnerability of Kenya’s Water Towers to Future Climate Change: An Assessment to Inform Decision Making in Watershed Management

Recent trends show that in the coming decades, Kenya’s natural resources will continue to face significant pressure due to both anthropogenic and natural stressors, and this will have greater negative impacts on socio-economic development including food security and livelihoods. Understanding the impacts of these stressors is an important step to developing coping and adaptation strategies at every level. The Water Towers of Kenya play a critical role in supplying ecosystems services such as water supply, timber and non-timber forest products and regulating services such as climate and water quantity and quality. To assess the vulnerability of the Water Towers to climate change, the study adopted the IPCC AR4 framework that defines vulnerability as a function of exposure, sensitivity, and adaptive capacity. The historical trends in rainfall indicate that the three Water Towers show a declining rainfall trend during the March-April-May (MAM) main rainy season, while the October-November-December (OND) short rainy season shows an increase. The temperature patterns are consistent with the domain having a common rising trend with a rate in the range of 0.3°C to 0.5°C per decade. Projection analysis considered three emissions scenarios: low-emission (mitigation) scenario (RCP2.6), a medium-level emission scenario (RCP4.5), and a high-emission (business as usual) scenario (RCP8.5). The results of the high-emission scenario show that the annual temperature over the Water Towers could rise by 3.0°C to 3.5°C by the 2050s (2036-2065) and 3.6°C to 4.8°C by the 2070s (2055-2085 results not presented), relative to the baseline period 1970-2000. The findings indicate that exposure, sensitivity, and adaptive capacity vary in magnitude, as well as spatially across the Water Towers. This is reflected in the spatially variable vulnerability index across the Water Towers. Overall vulnerability will increase in the water towers leading to erosion of the resilience of the exposed ecosystems and the communities that rely on ecosystem services these landscapes provide.

Importance and vulnerability of water towers across Northwest China

High mountains(known as water towers)in the arid areas of Northwest China(ARNWC)are major suppliers of water resources for the downstream oasis region,where large populations and economic activities are concentrated.Studies on both water supply and water demand in central Asia including ARNWC have been explored in recent decades,but a precise study on the importance and vulnerability of fine-scale water towers still needs to be conducted,because oases are isolated each other and each oasis has its own specific tower(s).Here we ranked the importance of water tower units(WTUs)using a simplified water tower index(WTI)based on water amount of supply/demand side at a fine river basin scale.Then the vulnerability of these WTUs is assessed with the consideration of future changes in climate,population.GDP,water stress,etc.We con eluded that the WTU of the Mid-branch Rivers of the Junggar Basin is the most important with the highest WTI.while the Yarkant River Basin is the most vulnerable.The WTUs such as the Yarkant,Hotan and Kaxgar of the Tarim River Basin as well as the Hei River of the Hexi Corridor are important at present and vulnerable under a considerable pressure from future climate change scenarios.To respond to these opportunities and risks,it is better to reduce the proportion of the primary industry appropriately,improve the efficiency of water use and strengthen the supervision of water resources utilization,especially in the industrial and urban planning as well as ecological engineering projects.

Contribution of the cryosphere to runoff in“Chinese water tower”based on environmental isotopes

Cryospheric meltwater is an important runoff component and it profoundly influences changes in water resources in the Tibetan Plateau.Significant changes in runoff components occur in the three-river headwater region(TRHR),which is an important part of“Chinese Water Tower”due to climate warming.However,these effects remain unclear owing to the sparse and uneven distribution of monitoring sites and limited field investigations.Quantifying the contribution of cryospheric meltwater to outlet runoff is a key scientific question that needs to be addressed.In this study,we analyzed 907 precipitation,river water,ground ice,supra-permafrost water,and glacier snow meltwater samples collected from October 2019 to September 2020 in the TRHR.The following results were obtained:(1)There was significant spatio-temporal variation in stable isotopes in different waters;(2)The seasonal trends of stable isotopes for different waters,the relationship between each water body and the local meteoric water line(LWML)confirmed that river water was mainly recharged by precipitation,supra-permafrost water,and glacier snow meltwater;(3)Precipitation,supra-permafrost water,and glacier snow meltwater accounted for 52%,39%,and 9%of river water,respectively,during the ablation period according to the end-member mixing analysis(EMMA);(4)In terms of future runoff components,there will be many challenges due to increasing precipitation and evaporation,decreasing snow cover,glacier retreat,and permafrost degradation.Therefore,it is crucial to establish the“star-machine-ground”observation networks,forecast extreme precipitation and hydrological events,build the“TRHE on the Cloud”platform,and implement systematic hydraulic engineering projects to support the management and utilization of water resources in the TRHR.The findings of environmental isotope analysis provide insights into water resources as well as scientific basis for rational use of water resources in the TRHR.

Analysis of fouling characteristic in enhanced tubes using multiple heat and mass transfer analogies

This paper provides a comprehensive analysis on cooling tower fouling data taken from seven 15.54 mm I.D. helically ribbed, copper tubes and a plain tube at Re = 16000. There are two key processes during fouling formation： fouling deposition and fouling removal, which can be determined by mass transfer and fluid friction respectively. The mass transfer coefficient can be calculated through three analogies： Prandtl analogy, VonKarman analogy, and Chilton-Colburn analogy. Based on our analyses, Von-Karman analogy is the optimized analogy, which can well predict the formation of cooling tower fouling. Series of semi-theoretical fouling correlations as a function of the product of area indexes and efficiency indexes were developed, which can be applicable to different internally ribbed geometries. The correlations can be directly used to assess the fouling ootential of enhanced tubes in actual coolinu tower water situations.