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| Titel |
Model Sensitivity to Parameters in the Simple 1-D Land-Atmosphere Model |
| VerfasserIn |
C. Liang, F. Van Ogtrop, V. Willem |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250061765
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| Zusammenfassung |
| Large scale effects are generally more important to the regional climate than local effects,
such as land cover. However there is rarely any comparison of the two types of
effects due to the complexity of the land-atmosphere system and the difficulties in
controlling different climate drivers. Here we look into this matter from a model
perspective.
The modified simple 1-D land-atmosphere model based on D’Andrea (2006) and
Baudena (2008) is used to investigate the relative sensitivity of climate variables (air
temperature and precipitation) to the external forcing and local forcing. The model has two
properties: firstly, it is an equilibrium model and secondly, it requires a small set of
parameters. Therefore, this model is suitable for sensitivity analysis in which the effect of
change in one factor can be isolated. In this study, we perform sensitivity analysis on the
effects of four parameters. External forcing is represented by solar radiation (100 - 800 W
m2) and moisture influx (0 - 1 mm hr-1) to the region. Local forcing is represented by the
initial leaf area index (LAI, 0 - 10) and the initial soil wetness (0.13 - 0.63). A normalized
index is used to access the sensitivity of the model outputs to the parameters. The index is
defined as
SI = dmax –dmin,
Dmean -
r
where dmax and dmin represent the local extremes; Dmean is the mean value for the whole
domain and r is the proportion of the whole domain from which the local extremes are
taken.
Precipitation and air temperature output both responded nonlinearly to the tested
parameters. Precipitation is resistant to changes when parameters are near to the lower end of
value ranges until a threshold is hit. On the other hand, temperature is more sensitive to the
low parameter values than the high parameter values. Hence, precipitation is suppressed and
temperature remains high due to lack of vegetation cover, or low soil moisture, or negligible
moisture influx from outside the region. Both precipitation and temperature are low when
radiation is insufficient (in this case, < 456 W m2). For the tested range, the system reveals
that both the initial soil moisture as shown by D’Andrea (2006) and other conditions can
lead to multiple equilibriums. The sensitivity indexes show that precipitation is
generally more sensitive to the changes in radiation and moisture influx, both with SI
> 2 in the middle ranges. The sensitivity of precipitation to the changes in soil
wetness and LAI are below 0.5. This could be an indication that external forcing is
more important than local forcing in determining the local climate. However, the
results also suggest the local effects can contribute to the local climate variation. |
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