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Quantifying the Role of Snowmelt in Stream Discharge in an Alaskan Watershed

Inspired by fellow science social on publication and citation, I decided to write a few short introduction posts on my recent publications.

Aside to promote my research, I also want to explain the research in depth for those who do not have a background in related research.

My first talk is about my paper titled "Quantifying the Role of Snowmelt in Stream Discharge in an Alaskan Watershed: An Analysis Using a Spatially Distributed Surface Hydrology Model". You can find the abstract of this paper from "https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017JF004214"

As the introduction explained, the major motivation of this study is due to the sensitivity of cryosphere to the warming climate. In general, the climate change community all agree that the high latitudes are more vulnerable to the global warming. If the global temperature increases, lots of snow cover and glacier may disappear. In fact, this is happening right now and reported by numerous observations. (http://science.sciencemag.org/content/356/6338/580) However, the complexity of climate change also implies that local climate can be changed dramatically even though the overall snow cover is decreasing (https://www.nature.com/articles/nature13625).

Not only snow and glacier are our major concerns, but also carbon. It is known huge amount of carbon is stored in the frozen soil (permafrost). Due to the warming, these carbon could be released into the biosphere. Similar to foil fuel, this is almost a one way process. Once deep soil carbon is released into the biosphere, it is unlikely we can reverse this process because it took hundreds to thousands of years to form stable permafrost. In this process, ancient microbe may also be released.
(http://www.bbc.com/earth/story/20170504-there-are-diseases-hidden-in-ice-and-they-are-waking-up)

To understand what kind of world we may face in the future is a major question we want to answer. One of the tools we use very often is computer model simulation. However, to simulate such a complex Earth System, there is a lot of work to do.

When I looked at the climate system in the high latitudes, i.e. Alaska, the first impression is the hydrology. Without improving our understanding of the hydrology system in Alaska, we cannot really improve understanding of other processes (e.g. carbon cycle).

In this study, we decided to develop a hydrology model to simulate the hydrology system using a fully distributed hydrological model (PRMS). Details of this model can be found from (https://wwwbrr.cr.usgs.gov/projects/SW_MoWS/PRMS.html)

While there are many challenges in hydrology in Alaska, we only focused on snow dynamics currently because snow plays an important role apparently.

 Figure 1. The hydrological network of the study area.


The simulation was driven by precipitation and temperature. Soil type and vegetation coverage, etc. are also used to set up the parameter distribution. The core processes we are interested in are the formation, compact and melt of snow. We also looked into the contribution of snowmelt to the stream discharge.

Our simulations have shown that lots of changes are happening unseen in our study area. First, the seasonal pattern of stream discharge is changing due to decrease in snowmelt in spring.

Second, snow cover in the high elevation (near permanent snow line or glacier) is decreasing. Basically it also means glacier is also reducing.

Third, the snow pack thickness in early spring is decreasing, which results in decreasing snowmelt in following months.


Figure 2. The simulated snowpack water equivalent (SWE) during the calibration and evaluation period.

We also approximated the timing of snowmelt onset. Our analyses have shown that snow pack "woke up" earlier for 2 day during the most recent decade. Besides, because of the prolonged "warming", snowmelt lasts longer as well, which originates near the glacier boundaries without surprise.
Figure 3. The start and end of snowmelt during the simulation period.

While we didn't see significant trend in total discharge over the short period simulation. Partly it is because of the interplay of decreasing snowpack and increasing melt from glacier. We conclude that hydrology system in Alaska is undergoing drastic changes under the warming climate.

The winter may lasts long for Alaskans, but it is definitely getting shorter and shorter, and we are not sure whether that is good news or not.



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