Twelve mountainous basins of the Vitim Plateau (Eastern Siberia, Russia) with
areas ranging from 967 to 18 200 km
Increasing intensity and number of forest fires in Russia are becoming a serious threat (Assessment Report on Climate Change, 2008). Though the studies of fire impact on environment have a long history in Russia, they mostly aim to assess the changes of vegetation (Lytkina, 2005), soil and permafrost (Tarabukina and Savvinov, 1990) or snow cover properties (Sabaeva, 2006) after fire and describe/predict the processes of forest succession and transformation of species diversity resulting from different types of fires (Isaev, 2011; Kharuk et al., 2008). Despite the fact that the effects of fire on catchment runoff response may be disproportionately strong compared to the area of burnt-out forest (Moody et al., 2008), the studies of those, such as abrupt changes of hydrological regime or the intensification of erosion processes that can lead to catastrophic flooding and even debris flows (Huscroft et al., 2004), are practically absent in Russia. Studies examining the impacts of clearcutting on hydrology are of some relevance, but are not entirely analogous with the impacts of fire on hydrological response (Onuchin et al., 2009, 2014; Krestovsky, 1986).
The characteristics of the basins under study.
a/b, c/d, e/f, g/h are the pairs of basin analogues.
Following the studies by Lebedeva et al. (2014) and Semenova et al. (2015) who detected a short-term effect of fire on a small mountainous catchment in the Vitim River basin which resulted in significantly increased summer flow, this research aimed to broaden the scope of previous investigations from one basin to a larger area to reveal the similarities or differences of basins response to fire events depending on the size of catchments, share of burnt area and post-fire hydrometeorological conditions. We also developed the scenario of landscape transformation after fire, assigned the parameters of hydrological model accordingly and conducted simulations of daily flow for the Amalat River basin impacted by fire in 2003 for pre-fire and post-fire period. The difficulty of the research was conditioned by the scarcity of runoff data, the unrepresentativeness of precipitation measurements for vast mountainous territories and the absence of any specific observations.
The study catchments are located in the Transbaikal region of Russia which is
a large and remote mountainous area to the east of the Baikal Lake (Fig. 1).
It is characterized by high variety of climate and landscape conditions and
forest fires are regularthere. Most part of the Vitim Plateau, the
mountainous area where the left tributaries of the Vitim River go through,
was subject to extensive forest fires in the spring of 2003. Based on monthly
gridded 500 m MODIS Burned Area Product (MCD45) we delineated twelve gauged
catchments with basin areas ranging from 969 to 18 200 km
Very limited data is available for this remote region. There are twelve
runoff gauges from which data could be used for long-term analysis and less
than twenty meteorological stations with continuous series of observation
covering about 70 000 km
The assessment of fire effect on flow is conducted based on the use of
basin-analogues which have significant correlation of flow with “burnt”
watersheds in stationary (pre-fire) period. We assume that fire impact should
produce an outlier of this established dependence. In the case of very
limited datathe relativeness of the term “basin-analogue” should be taken
into consideration. The effects of local precipitation on runoff generation
are very high in mountains, so even in similar landscape conditions it turned
out to be difficult to select basin-analogues. In this case the most reliable
correlation of flow is observed flow from subbasin gauges. Four watersheds
with extensive share of burnt area are the upper parts of larger basins.
Those four pairs of watersheds were treated as the basin-analogues as they
have meaningful mutual correlation of flow during warm season
(June–September) with the values of
The scheme of studied area.
Two fire-affected basins, namely the Tcipa River at Tcipikan and the Karenga River at Tungokochen with 33 and 72 % share of burnt area, respectively did not behave differently to pre-fire conditions during 2003. However, summer flow at those two basins does not have close dependences on precipitation which are observed at nearest meteorological stations. Therefore, any short-term changes of water balance were not detected for the Tcipa and Karenga Rivers watersheds based on available monthly data.
On the contrary, two other basins, the Vitimkan River at Ivanovsky and Amalat
River at Ust'-Antose with 78 and 22 % share of burnt area, displayed
expected fire-affected behavior. Strong correlation between flow for burnt
and analogue watersheds within the stationary period is broken by 2003
dependence outlier. Summer flow during the warm season following spring fire
was increased at those basins. According to Figs. 2 and 3 summer
(June–September) flow in 2003 is heightened approximately by 40 mm at the
Amalat River and more than 100 mm at the Vitimkan River. The presence of
fire impact is confirmed by the defection of runoff – precipitation
dependence as well. In Figs. 2 and 3 one can see that during stationary
periods summer flow has strong, though not linear, dependence on summer
precipitation. 2003 is an outlier of such dependences at both basins
suggesting that fire was the reason of changed patterns of flow.
Interestingly, burnt area seems not to be the main factor determining basins
response. The increase of flow at the Amalat River basin with 22 % of
burnt area is relatively higher (from expected 100 to observed 150 mm) than
at the Vitimkan River basin (78 % burnt area) where 41 % flow
increase was estimated by Semenova et al. (2015).We assume that relatively
small size of the basins (969 and 2100 km
The dependence of summer (June–September) flow at burnt and analogue basins; the dependence of summer flow at burnt basin on summer sum of precipitation at nearest meteorological station during stationary conditions and the dependences outliers caused by fire. Here burnt basin: Amalat River at Ust'-Antose (3130), analogue basin: Amalat River at Rassoshino (3131) and meteorological station – Ust'-Antose. 1966–1990 and 2000–2011.
The dependence of summer (June–September) flow at burnt and analogue basins; the dependence of summer flow at burnt basin on summer sum of precipitation at nearest meteorological station during stationary conditions and the dependences outliers caused by fire. Here burnt basin: Vitimkan River at Ivanovsky (3109), analogue basin: Vitim River at Romanovka (3096) and meteorological station – Karaftit. 1967–2004.
The lack of basin-analogues for the other three basins (the Zaza, Yumurchen and Konda Rivers), pronounced hysteresis type of the basins response to precipitation and generally drier conditions did not reflect the assessment of immediate fire impact on flow at monthly scale even though the shares of burnt area were rather high (49, 67 and 41 %, respectively).
Though hydrological models may be applied to detect the transformation of flow characteristics due to climate or landscape changes (ex., Seibert et al., 2010), future projections of hydrological behavior in non-stationary conditions based on the results of hydrological modelling are generally questionable (Semenova and Beven, 2015). This is because calibration of model parameters has become almost inevitable and rarely challenged part of modelling procedure.
Schematization of the Amalat River basin for hydrological modelling.
Observed and simulated hydrographs for the Amalat River at Ust'-Antose with
“stationary” parameters:
The dependence of observed and simulated flow depth in August for the Amalat River at Ust'-Antose with “stationary” parameters.
Forest fires impact watersheds unexpectedly, their response to disturbance depending on many factors including the post-fire meteorological situation (Moody et al., 2013) and usually there are not enough data to calibrate the models for the post-fire environment. That is why new methods based on a priori comprehension of non-stationary processes are required for reliable projections of hydrological response.
Semenova et al. (2015) used the Hydrograph model (Semenova et al., 2013; Vinogradov et al., 2011) to detect and estimate immediate fire impact on flow and proposed the use of dynamic approach for hydrological modelling in post-fire environment for the Vitmkan River basin where only standard hydrometeorological data was available.
Comparison of observed and simulated hydrographs with the parameters assessed for pre-fire and post-fire periods. The Amalat River basin, 2003.
In the current study we conducted simulations of runoff formation processes for the Amalat River basin. It is situated close to the Vitimkan River basin (Fig. 1) and characterized by similar landscape conditions, therefore the set of the Hydrograph model parameters previously derived by Semenova et al. (2015) was applied, as well as the scenario of landscape properties transformation after fire in 2003. The scheme of Representative Points (RP) and runoff formation complexes (RFC), burnt area and the location of meteorological stations and runoff gauge for the Amalat River basin are shown at Fig. 4.
Continuous simulations of flow with pre-fire (“stationary”) parameters were
performed for 1966–2012 period (including fire year 2003) with
Nash-Sutcliffe criteria varying from
Next step of the research was the application of the model parameters developed for post-fire conditions. These model parameter values were based on literature review of landscape properties changes as described by Semenova et al. (2015) and applied for the Amalat River here. The results of flow simulations with stationary and non-stationary parameters are presented in Fig. 7. They suggest the intensification of soil thaw due to change of surface energy balance (Jiang et al., 2015) and reduction of infiltration rate and evapotranspiration which in general lead to the increase of surface and preferential flow in soil horizons destroyed by fire (Koch et al., 2014) during summer flood events.
Siberian basins are subject to regular forest fires. Often little information is available about fires except their timing and areal distribution. Observed changes of hydrological response at burnt watersheds may serve as the only indirect quantitative evidence of soil, vegetation and permafrost transformation due to fire impact. The analysis of hydrological data and process scenario modelling may be used to reveal possible changes of landscape properties.
Though Semenova et al. (2015) demonstrated for the Vitimikan River that short-term impact of fire on hydrological processes can be significant during extreme precipitation events, in most cases of limited meteorological data which does not allow for exact estimation of precipitation input at a mountainous watershed, the effects of fire on flow could be difficult to determine.
Available monthly flow and precipitation data for the studied region allowed for qualitative detection of fire short-term impact on flow at two basins from twelve studied basins in 2003. The impact expressed in increase of summer flow following the fire up to a 40–50 %.
The combination of several factors could lead to the short-term transformation of hydrological regime, such as severity and extent of soil-vegetation disturbance and large precipitation events. Possible changes of physical mechanisms of runoff formation are discussed by Semenova et al. (2015), but the specification of each factor's input in those changes is impossible without additional information (for example, satellite data or field studies).
The approach to simulate changed hydrological processes based on a priori interpretation of possible landscape transformations used in this study is promising for application in hydrological modelling under non-stationary conditions, though very few models independent of calibration procedure can utilise such an approach. The Hydrograph model applied herein is one of them.
The study was partially supported by Russian Foundation of Basic Research (projects no. 14-05-00665 and 14-05-31194).