| 1. |
- Berndtsson, R., et al.
(författare)
-
Solar-climatic relationship and implications for hydrology
- 2001
-
Ingår i: Nordic Hydrology. - 0029-1277. ; 32:2, s. 65-84
-
Tidskriftsartikel (refereegranskat)abstract
- Research during the latest years has indicated a significant connection between climate and solar activity. Specifically, a relationship between Northern Hemisphere air temperature and sunspot cycle length (SCL) has been shown. By using monthly SCL and land air temperature from 1753-1990 (238 years) we show that this relationship also holds for a single observation point in south of Sweden. Using data after 1850 yields a statistically significant linear correlation of 0.54 between SCL and mean temperature. Furthermore, we show that there are indications of a low-dimensional chaotic component in both SCL and the interconnected mean land air temperature. This has important implications for hydrology and water resources applications. By pure definition of chaos this means that it is virtually impossible to make long-term predictions of mean temperature. Similarly, because of the strong connection between temperature and many hydrological components, it is probable that also long-term water balance constituents may follow chaotic trajectories. Long-term projections of water resources availability may therefore be impossible. Repeated short-term predictions may, however, still be viable. We exemplify this by showing a technique to predict interpolated mean temperature 6 and 12 months ahead in real time with encouraging results. Improving the technique further may be possible by including information on the SCL attractor. To summarize, research into the possible existence of chaotic components in hydrological processes should be an important task for the next years to come.
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Sivakumar, B., et al.
(författare)
-
Dynamics of monthly rainfall-runoff process at the Göta basin : A search for chaos
- 2000
-
Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 4:3, s. 407-417
-
Tidskriftsartikel (refereegranskat)abstract
- Sivakumar et al. (2000a), by employing the correlation dimension method, provided preliminary evidence of the existence of chaos in the monthly rainfall-runoff process at the Göta basin in Sweden. The present study verifies and supports the earlier results and strengthens such evidence. The study analyses the monthly rainfall, runoff and runoff coefficient series using the nonlinear prediction method, and the presence of chaos is investigated through an inverse approach, i.e. identifying chaos from the results of the prediction. The presence of an optimal embedding dimension (the embedding dimension with the best prediction accuracy) for each of the three series indicates the existence of chaos in the rainfall-runoff process, providing additional support to the results obtained using the correlation dimension method. The reasonably good predictions achieved, particularly for the runoff series, suggest that the dynamics of the rainfall-runoff process could be understood from a chaotic perspective. The predictions are also consistent with the correlation dimension results obtained in the earlier study, i.e. higher prediction accuracy for series with a lower dimension and vice-versa, so that the correlation dimension method can indeed be used as a preliminary indicator of chaos. However, the optimal embedding dimensions obtained from the prediction method are considerably less than the minimum dimensions essential to embed the attractor, as obtained by the correlation dimension method. A possible explanation for this could be the presence of noise in the series, since the effects of noise at higher embedding dimensions could be significantly greater than that at lower embedding dimensions.
|
|
| 7. |
- Tsutsumi, A, et al.
(författare)
-
Surface and subsurface water balance estimation by the groundwater recharge model and a 3-D two-phase flow model
- 2004
-
Ingår i: Hydrological Sciences Journal. - 0262-6667. ; 49:2, s. 205-226
-
Tidskriftsartikel (refereegranskat)abstract
- Land development often results in adverse environmental impact for surface and subsurface water systems. For areas close to the coast, land changes may also result in seawater intrusion into coastal aquifers. Due to this, it is important to evaluate potential adverse effects in advance of any land development. For evaluation purposes a combined groundwater recharge model is proposed with a quasi three-dimensional unconfined groundwater flow equation. The catchment water balance for a planned new campus area of Kyushu University in southern Japan, was selected as a case study to test the model approach. Since most of the study area is covered with forest, the proposed groundwater recharge model considers rainfall interception by forest canopy. The results show that simulated groundwater and surface runoff agree well with observations. It is also shown that actual evapotranspiration, including rainfall interception by forest canopy, is well represented in the proposed simulation model. Several hydrological components such as direct surface runoff rate, groundwater spring flow rate to a ground depression, trans-basin groundwater flow etc., were also investigated.
|
|
| 8. |
|
|
| 9. |
- Yasuda, H., et al.
(författare)
-
Characterizing preferential transport during flood irrigation of a heavy clay soil using the dye vitasyn blau
- 2001
-
Ingår i: Geoderma. - 0016-7061. ; 100:1-2, s. 49-66
-
Tidskriftsartikel (refereegranskat)abstract
- Common irrigation procedures in many parts of the world involve flood irrigation. Observations during recent years have, however, indicated that preferential flow may be an important phenomenon that could affect the outcome of both irrigation and fertilizer application for this irrigation type. To analyze and visualize solute transport by preferential flow mechanisms, field experiments were carried out at the Cherfech Agricultural Research Station in northern Tunisia. Paths of solute transport were investigated by a 0.05-m ponded pulse of Vitasyn Blau dye allowed to infiltrate into the unsaturated heavy clay soil. Two experimental plots were prepared for the infiltration of dye by leveling the surface. Leveling was done to have similar surface conditions at the two plots. After infiltration, a trench was dug at the border of the dye-injected region to document the dye patterns vertically and horizontally. The patterns indicated strong dependence on the horizontal structure of the soil. In general, the dye was to a major extent transported along distinct cracks and ped faces in the prismatic silty clay. Only the upper 0-0.05 m depth of the tilled soil had almost a complete dye coverage. Below this depth, preferential dye patches start to develop and dye coverage is rapidly decreasing to below 50% at 0.15 m depth. Even though transport through the prismatic silty clay mainly followed cracks between the prisms, it is estimated that only 10-20% of these vertical cracks are active in conducting solutes. The results from the present study have implications for soil management in areas using flood and furrow irrigation with soils susceptible to preferential flow. Tillage depth is a factor that is likely to have a great impact on the amount of water that reaches the soil matrix. Increasing tillage depth and other management practices that break up the structure and make the soil more homogeneous will increase the efficiency of irrigation and reduce the susceptibility for preferential flow.
|
|
