Climate Change

The impact of global climate change on water supply is a major area of research. Climate change can be simulated with SWAT+ by manipulating the climatic input that is read into the model (precipitation, temperature, solar radiation, relative humidity, wind speed, potential evapotranspiration and weather generator parameters). A less time-consuming method is to set adjustment factors for the various climatic inputs.

SWAT+ will allow users to adjust precipitation, temperature, solar radiation, relative humidity, and carbon dioxide levels in each subbasin. The alteration of precipitation, temperature, solar radiation and relative humidity are straightforward:

Rday=Rday(1+adjpcp100)R_{day}=R_{day}*(1+\frac{adj_{pcp}}{100}) 1:4.2.1

where RdayR_{day} is the precipitation falling in the subbasin on a given day (mm H2_2O), and adjpcpadj_{pcp} is the % change in rainfall.

Tmx=Tmx+adjtmpT_{mx}=T_{mx}+adj_{tmp} 1:4.2.2

where TmxT_{mx} is the daily maximum temperature (°C), and adjtmpadj_{tmp} is the change in temperature (°C).

Tmn=Tmn+adjtmpT_{mn}=T_{mn}+adj_{tmp} 1:4.2.3

where TmnT_{mn} is the daily minimum temperature (°C), and adjtmpadj_{tmp} is the change in temperature (°C).

Tav=Tav+adjtmp\overline T_{av} =\overline T_{av} +adj_{tmp} 1:4.2.4

where Tav\overline T_{av} is the daily mean temperature (°C), and adjtmpadj_{tmp} is the change in temperature (°C).

Hday=Hday+adjradH_{day}= H_{day}+ adj_{rad} 1:4.2.5

where HdayH_{day} is the daily solar radiation reaching the earth’s surface (MJm2MJ m^{-2}), and adjradadj_{rad} is the change in radiation (MJm2d1MJ m^{-2} d^{-1}).

Rh=Rh+adjhmdR_h=R_h +adj_{hmd} 1:4.2.6

where RhR_h is the relative humidity for the day expressed as a fraction, and adjhmdadj_{hmd} is the change in relative humidity expressed as a fraction.

SWAT+ allows the adjustment terms to vary from month to month so that the user is able to simulate seasonal changes in climatic conditions.

Changes in carbon dioxide levels impact plant growth. As carbon dioxide levels increase, plant productivity increases and plant water requirements go down. The equations used to account for the impact of carbon dioxide levels on plant water requirements are reviewed in Chapters 2:2 and 5:2. When carbon dioxide climate change effects are being simulated, the Penman-Monteith equation must be used to calculate potential evapotranspiration. This method has been modified to account for CO2 impacts on potential evapotranspiration levels.

Table 1:4-2: SWAT+ input variables that pertain to climate change.

RFINC(mon)

adjpcpadj_{pcp}: % change in rainfall for month

.sub

TMPINC(mon)

adjtmpadj_{tmp}: increase or decrease in temperature for month (°C)

.sub

RADINC(mon)

adjradadj_{rad}: increase or decrease in solar radiation reaching earth’s surface for month (MJ m2^{-2})

.sub

HUMINC(mon)

adjhmdadj_{hmd}: increase or decrease in relative humidity for month

.sub

CO2

CO2CO_2: carbon dioxide level in subbasin (ppmv)

.sub

IPET

Potential evapotranspiration method

.bsn

Last updated