Responses to climate variability in different catchments

Abstract:

Abstract Long-term (>70 year) hydrological data sets for large river catchments are analyzed to assess the effects of climatic variability.

In this study we analyzed the response of long term runoff to preceden climatic conditions at long term scales of 70 years in 6 large river catchments in different parts of the Earth. Two types of catchment responses to climate change are detected - increasing and decreasing of water resources.

Introduction

The Earth's climate has changed many times throughout its geologic history.

Climate variability causes either a cooling with accompanying process of accumulation of water resources in the form of glaciers or warming and active intensification of water cycle due to rapid atmosphere circulation.

Watershed-scale responses to climate change could include reductions in snowpack and soil moisture, changes to snowmelt timing, and alterations to streamflow, those changes will vary in different river water basins. The hydrological responses of different geographical regions of the Earth to potential climate change are different, depending on the dominant physical processes of that particular region.

Climate variability and behavior of catchments.

The major driving force of the hydrologic cycle is solar heating which provides the continuous movement of water on the Earth. The mass water on Earth remains constant over time but the redistribution of the water among polar ice caps and glaciers, fresh water, saline water and atmospheric wateris variable depending on a wide range of variables. The river runoff comes from total watershed area and is concentrated into a single channel that acts like an integrator. River flow provide a single-point measurement; giving both large-scale averaging in catchments and amplification. River discharge measurement over the long term period can be also considered as a cumulative effect of local weather parameters such as temperature, wind, rainfall, snow, glaciers melting and ocean currents, as well as interaction among these.

When the Sun has fewer sunspots, it gives off less energy, less energy makes its way to Earth, and our planet cools down. Sunlight is more intense at the equator than at the poles, creating a marked difference in temperature, which causes energy to spread out from the hotter equator towards the colder higher latitudes. This energy transport drives both atmospheric circulation and ocean currents. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the Earth's surface, completing the water cycle. The Earth rotation on its axis and solar energy causes an effect of prevailing wind patterns as Easterlies and Westerlies. The direction of the prevailing wind will affect how much water it carries. In this way a geomorphology plays important role for water formation processes (e.g. mountain ranges are the interceptors for wind intrusion and clouds).

Taking into account above described there were averaged river runoffs for one solar cycle. In other words - one averaged solar cycle (sunspot cycle) is equal to one unit of measurement for both: solar activity and river runoff.

The result of these calculations presents Fig.1.

As seen from Fig.1, temperature rise in the last century in case of the Yangtze and the Godavari rivers leads to different catchment responses. Intensification of atmosphere circulation due to climate change brings more monsoons with evaporated water- increase the Godavari discharge, but the Himalaya mountain range intercept this movement and in the Tibetan Plateau takes place stable decrease of melting glacier water and eventually the discharge of Yangtze River.Fig.1 Long- term river runoff trends.

The Songhua Jiang, the Amur, Mississippi and Danube rivers indicate also different trends in catchments behavior.

Relationship of solar activity to catchments responses.

Annual averaged river runoffs are compared with averaged Wolf numbers (both averaged for one solar cycle). This method allows detecting an influence of solar activity on water formation process. There are significant positive relationships between solar activity and river runoff of the rivers Godavari, Songhua Jiang and Mississippi (Fig.1.b, c, e). The correlation between solar activity and rivers runoff consist more than 0, 7. An increase of solar activity does actually increase these large rivers discharge. This positive relationship is actually conventional. When the Sun has many sunspots it gives more energy, more energy makes its way to Earth, and our planet will warm, warm air increases the evaporation process, and leads to intensification of hydrological cycle.

Surprisingly, the rivers Yangtze, Amur and Danube (Fig.1, a, d, f) show a steady trend of rivers runoff decrease.

In all calculations were used raw datasets of river runoff. It was not taken into account a water volume was held by dams. Such correction could be significantly improving correlation between solar activity and river runoff.

Solar activity and air temperature trends.

In all studied river catchments areas were observed increasing of air temperature. The same method described above was applied for finding the connection between the solar activity and air temperature in watersheds.

Temperature trends in the Yangtze River watershed in dependence on solar activity in following weather stations:

Kunming: T= -0,02W + 17, 02, r=0, 87

Wuhan: T = -0,02W + 18, 09, r = 0, 83

Yichang: T = -0,02W + 18, 17, r= 0, 77

Temperature trends in Hindustan Peninsula:

Hyderabad: T = 0,01W + 25, 73, r= 0, 75

Bangalore: T = 0,02W + 22, 99, r=0, 88

Temperature trend in the Songhua Jiang River watershed:

Harbin: T= 0,02W+ 2,530

Temperature trend in the Amur River watershed:

Blagoveshensk: T= 0,02W+ 2, 53, r= 0, 77

Temperature trend in the Mississippi River watershed:

Minneapolis: T= 0,03W + 11, 14, r=0, 76

St Cloud : T = 0,01W+ 5,296, r=0,77

Temperature trend in Danube River catchment:

Wien, T= 0,02W + 8, 11, r=0, 89

Budapest, T= 0,02W + 8, 85, r= 0, 88

Where T - air temperature in °C, W-sunspots number, r - coefficient of correlation.

Discussion

Climate change effect acts in different ways in various catchments. In accordance with NASA forecasting the next two solar cycles will be below average in intensity. This actually will lead to a decrease of the temperature on 1-1, 5 degree in both averaged solar cycles.

Air temperature decrease will lead to an accumulation of water in form of ice on the continents. Rivers discharge on watershed scale will be change in dependence from geographical location.

In catchments area of rivers Yangtze, Amur and Danube will be more floods and in watersheds of rivers Godavari, Songhua Jiang and Mississippi will be more droughts during 24 and 25 solar cycles - up to 2030.

The source of data: Global Runoff Data Centre, Koblenz, Germany, NASA Surface Temperature Data.