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book/thesis_projects/BSc/2025_Q3_IschaHollemans_CEG/Report/3_historical_droughts.md

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@@ -27,18 +27,19 @@ date where the discharge falls below the critical water flow of 66.5 m³/s. This
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and thus the beginning of a deficit. For each day onward, the algorithm calculates the difference
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between current discharge and the critical flow:
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$$D(t) = (Q(t) - Q_{crit})$$
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$$ D(t) = (Q(t) - Q_{crit}) $$
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If the value is negative, it stands for deficit. If the value is positive, it means that the hydrological system
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gets replenished. The severity of the deficit is quantified by taking the maximum cumulative water deficit
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which uses the following formula:
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$$D_{cum}(t) = \sum_{i=0}^{t} D(i)$$
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$$ D_{cum}(t) = \sum_{i=0}^{t} D(i) $$
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By using this for every timestep, the following list is created equation 3. The maximum cumulative deficit
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is eventually calculated using equation 4.
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$$D_{cum,list} = \left[ D_{cum}(1),D_{cum}(2), ..., D_{cum}(n) \right]$$
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$$D_{max} = \text{max} \left( |D_{cum,list(t)}| \right) \text{, } t \in [1,n]$$
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$$ D_{cum,list} = \left[ D_{cum}(1),D_{cum}(2), ..., D_{cum}(n) \right] $$
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$$ D_{max} = \text{max} \left( |D_{cum,list(t)}| \right) \text{, } t \in [1,n] $$
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The drought period is defined by the amount of time it takes for the system to replenish the amount of
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lost water. In figure 3, a visualisation of the length of a drought $T_{drought}$, and $D_{max}$ is displayed:

book/thesis_projects/BSc/2025_Q3_IschaHollemans_CEG/Report/4_future_droughts.md

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These cumulative distributions are then used for quantifying the difference between historical and future
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droughts in terms of return period. This is achieved by using the drought return period function used by
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Zhao, et al. (2017):
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$$T_D = \frac{N}{n\left( 1-F_D(d) \right)}$$
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$$T_S = \frac{N}{n\left( 1-F_S(s) \right)}$$
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$$ T_D = \frac{N}{n\left( 1-F_D(d) \right)} $$
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$$ T_S = \frac{N}{n\left( 1-F_S(s) \right)} $$
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The return period for duration is defined by $T_D$, and for severity (deficit) $T_S$. The length of the dataset is
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expressed by $N$, which is equal to 72 years. The number of drought observations is denoted by $n$. The
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To make sure that the modelled return periods are precise, the historical CMIP6 droughts are validated
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using the observed past droughts. The validation is displayed in figure 10:
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!figure10](figures/figure10.png)
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![figure10](figures/figure10.png)
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*Figure 10: Validation of the return periods for 1942-2014. The graphs show a significant discrepancy for
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both drought duration and deficit.*
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book/thesis_projects/BSc/2025_Q3_IschaHollemans_CEG/ischa/CMIP_Future_prediction.ipynb

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"id": "4839d59f-30b4-47b8-bbdd-694bbcf458cf",
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"metadata": {},
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"source": [
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"# CMIP Future prediction\n",
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"# Generating (CMIP6) future droughts\n",
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"\n",
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"This notebook is used to predict future discharge values for the Loire river at Blois. For these prediction, different climate scenarios are used: SSP126, SSP2455 and SSP585. These discharge values are then analysed using the drought analyser (Drought_analyser.ipynb) to assess the difference between past and future. "
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]

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