Keywords: package «bsts», structural model of time series, discharge, training and test samples, trends

Qualitative forecasting of river water levels is an important component for planning and functioning of various water-dependent sectors of the economy: agriculture and municipal services, hydropower, fisheries, shipping, etc. Forecasting of river daily discharges is based on both simple graphical methods and deterministic and stochastic models. The article is devoted to the use of the “bsts” package of the R programming language for modeling and forecasting daily discharges of the Desna River – Litky village. After decomposition of the time series of daily discharges was found that these series consist of three components: a trend, a seasonal component, and random fluctuations. In the process of creating the 'bsts' model, the main functions of the 'bsts' package, which form the various components of this model, were considered: add.seasonal, add.local.level, add.ar, add.local. linear.trend, add.semilocal. linear.trend and add.student.local.linear.trend. The results of modeling the daily discharges of the training and test samples were evaluated using five statistical indicators: residual.sd, prediction.sd, rsquare, relative.gof та МАРЕ, and also by the accumulated error curve of the next step. The optimal model is the “bsts” - model without predictors, which models daily discharges using the add.student.local.linear.trend function and random fluctuations. This model is suitable for short-term forecasting of daily discharges of the Desna River – Litky village during periods of their long and smooth increase or decrease, as well as during periods of stable low water levels. Forecasting daily discharges using the 'bsts' - model is based on a trend that relates this model to forecasting based on spring flood decline curves, which take into account the depletion of water reserves in the channel network, and trends that take into account the inertia of hydrological processes.

1. Krakovska, S. V., Palamarchuk, L. V, Gnatiuk, N. V., Shpytal, Т. M., Shedemenko, I. P. (2017). Changes in precipitation distribution in Ukraine for the 21st century based on data of regional climate model ensemble. Geoinformatika, 4, 62-74. http://nbuv.gov.ua/UJRN/geoinf_2017_4_9 [in Ukrainian].

2. Kulbida, M., Oliynyk, Z., Palamarchuk, L., Galytska, E. (2013). Precipitation regime in Ukraine for the decade 2002-2011. Physical Geography and Geomorphology, 1, 127-138. http://nbuv.gov.ua/UJRN/fiz_geo_2013_1_17 [in Ukrainian].

3. Lyalko, V. I., Yelistratova, L. A., Apostolov, A. A. (2014). Researches of problems of dryness in the territory of ukraine with use of land and satellite information. Ukrainian Journal of Remote Sensing, 2, 18-28. http://nbuv.gov.ua/UJRN/ukjdzz_2014_2_5 [in Ukrainian].

4. Malytska, L. V., Balabukh, V. O. (2020). Possible changes of climate conditions in Ukraine to the middle of the XXI century. Hydrology, hydrochemistry and hydroecology, 1 (56), 94-100. http://nbuv.gov.ua/UJRN/glghge_2020_1_12 [in Ukrainian].

5. Martazinova, V. F., Horodetska, N. S., Rybchenko, L. S., Savchuk, S. V., Hrebeniuk, N. P., Tatarchuk, O. H. (2022). Features of the current state of the temperature-humidity regimeof Ukraine since the beginning of the XXI century under the influence of changes of large-scale atmospheric circulation. Meteorology. Hydrology. Environmental monitoring, 2, 22-34. http://jnas.nbuv.gov.ua/article/UJRN-0001463853 [in Ukrainian].

6. Nazhmudinova, H. N. (2021). Anomalies of air temperature in Chernihiv region. Physical Geography and Geomorphology, 108. 44 (2), 49-55. https://doi.org/10.17721/phgg.2021.4-6.05 [in Ukrainian].

7. Palamarchuk, L, Sokur, K., Zabolotska, T. (2019). Dynamics of rainfall intensity and mesostructural characteristics of their fields in the warm period of the year in the plain part of Ukraine. Hydrology, hydrochemistry and hydroecology, 4 (55), 95-111. https://doi.org/10.17721/2306-5680.2019.4.8.

8. Pysarenko, V. M., Pysarenko, P. V., Pysarenko, V. V., Gorb, O. O., Chaika, T. O. (2019). Droughts in the context of climate changes in Ukraine. Bulletin of the Poltava State Agrarian Academy, 1, 134-146. http://nbuv.gov.ua/UJRN/VPDAA_2019_1_17 [in Ukrainian].

9. Pysetska S., Shcheglov, O. A., Grebenyuk, N. P. (2022). Space-time distribution of mass deposits of wet snow in the territory of Ukraine during 1991-2020 : collective monograph / edited by M. S. Malovany. Kyiv : Yaroshenko Y. V., 202-228. https://doi.org/10.51500/7826-23-0 [in Ukrainian].

10. Tymofeyev, V., Tatarchuk, O. On the monthly maximum precipitation amount in Ukraine in conditions of the current climate Visnyk of Taras Shevchenko National University of Kyiv. (Geography), 1 (63). 33-37. http://nbuv.gov.ua/UJRN/VKNU_geograf_2015_1_10 [in Ukrainian].

11. Boychenko, S. & Maidanovych, N. (2024). A century-long tendency of change in surface air temperature on the territory of Ukraine. Geofizicheskiy Zhurnal, 46 (2). https://doi.org/10.24028/gj.v46i2.297227

12. Budnik, S. V. (2019). Spatio-Temporal Change of Atmospheric Precipitation on Territory of North-West of Ukraine. Journal of Atmospheric Science Research, 2(4), 1-4. https://doi.org/10.30564/jasr.v2i4.1564

13. Polevoy, A., Barsukova, O., Husieva, K., Zhygailo, O., Volvach, O., Kyrnasivska, N., Tolmachova, A., Zhygailo, T., Danilova, N. & Kostiukievych, T. (2024). The Climate Change Impact on the Development of Droughts in Ukraine. Journal of Ecological Engineering, 25 (6), 194-205. https://doi.org/10.12911/22998993/187276

14. Pyasetska, S. & Shcheglov, O. (2023). The modern nature of changes in the average monthly air temperature during 2006-2020. Visnyk of V. N. Karazin Kharkiv National University. Series Geology. Geography. Ecology, 58, 217-230. https://doi.org/10.26565/2410-7360-2023-58-17

15. Semenova, I. & Vicente-Serrano, S. M. (2024). Long-term variability and trends of meteorological droughts in Ukraine. International Journal of Climatology, 44 (6), 1849-1866. https://doi.org/10.1002/joc.8416

16. Vyshnevskyi, V. І. (2025). Climate Change in Ukraine and its Consequences. Journal of Landscape Ecology, 18 (4), 150-174. https://doi.org/10.2478/jlecol-2025-0032

17. Zatula, V. (2024). Complex assessing of aridity in Ukraine. Visnyk of V. N. Karazin Kharkiv National University. Series Geology. Geography. Ecology, 61, 180-192. https://doi.org/10.26565/2410-7360-2024-61-15